We could only open with the self-timer of a particularly enterprising specimen of a Sulawesi crested black macaque (Macaca nigra) who took a series of photos of his big face smiling while fiddling with the equipment of an English photographer, in the northern island Indonesia.

The initial distrust of the equipment soon gave way to curiosity: "Before I could recover my camera, the group of macaques had made hundreds of shots, " explained the photographer. "At first they took a lot of pictures of teeth, " he said, "although most of the shots came out of focus" (look at two more photos of the episode).

As in a scene from the animated film "Finding Nemo" this green turtle from Maldives (Chelonia mydas) approached the British underwater photographer Adam Broadbent, who was framing it, with the most radiant smile.

More beautiful photos and lots of curiosity about turtles

The laughter of an Indonesian orangutan (Pongo pygmaeus). If until now it was thought that primates laughed only by imitation of man, now we know that it is not so. Researchers from the University of Portsmouth (England) enjoyed tickling around twenty orangutans, gorillas, bonobos and chimpanzees. Comparing their laughter to those of some children, they discovered that monkeys not only laugh like us, using the same physical mechanisms (the type of breathing, the emission of sound), but also for the same reasons, ie when they experience a emotion.

Our laughter, in other words, would derive directly from that of primates, even if the conformation of the larynx of monkeys prevents them from emitting the "ah-ah" typical of human laughter (for example, the sound of a chimpanzee's laughter resembles more than anything to a labored breathing).

Do you know why laughter is contagious?
All the most beautiful primate photos (look)

Initially in the primates, the gesture of uncovering the teeth was equivalent to a signal of threat. Only later, in the apes closest to man, this gesture became a sign of submission and not hostility.

Finally, in man, a smile has become a symptom of openness and a desire to make friends. Laughter was born from the smile accompanied by a vocalization: the oldest one probably resounded in the African savannah when the first men began to walk upright, 2 or 3 million years ago.

If laughter is widespread in anthropomorphic monkeys, humor remains a purely human prerogative.

The spotted hyena or hyena ridens (Crocuta crocuta) for the peculiarity of emitting a high-pitched sound similar to a hysterical human giggle. It does, to tell the truth, in situations of nervousness or to formulate a request for help: according to some researchers, each hyena would produce a specific sound that provides information on age and on one's social position. These signals would serve to put some order in the hierarchies of complex groups, which include 10 to 90 copies.

Do you know why they say "be a hyena"?

This full, satisfied and laughing face will soon change: in a few weeks the mouth of the tadpole will widen until it becomes as wide as the whole head, the body will separate into two distinct segments, head and trunk, and the long-awaited front paws will appear. At that point the little guy - here under the microscope - will be almost ready to leave the water and change "menu".

During the development phase, in fact, tadpoles are generally vegetarian and feed on the algae present inside their pond (some for reasons of adaptation, are born omnivores and are satisfied with the debris that settles on the bottom of the water). But upon completion of the metamorphosis the intestine changes to prepare itself for the new diet: the adult specimen, frog or toad, will be greedy for small invertebrates.

Don't miss the gallery dedicated to frogs

The "smile" of a polar bear (Ursus maritimus). Despite "friendly" appearances, white bears are rather solitary animals: the only moments of socializing are those that occur between a mother and puppies or between partners at the time of mating. For the rest, these mammals spend most of the time (over 65%) idling or traveling, swimming or walking, looking for food.

The "obliged" smile of an Antarctic pygoscelid (Pygoscelis antarcticus). This bird of the penguin family has a thin strip of black plumage that runs from one side of the head to the other, just below the beak. That's why in the photos, you always have the impression that you are smiling.

The most beautiful photos of penguins: go to the gallery

Some would say that you are sharpening your teeth while enjoying a tasty snack.

But for Todd Mintz, the underwater photographer who made this shot in the waters of the Bahamas, the lemon shark (Negaprion brevirostris) you see is "smiling".

To tell the truth the beast, which can reach 3 and a half meters in length, is known for its dangerous and sudden attacks on divers and surfers in the shallow waters of the American coasts. Named for the yellowish color of its skin, it has hooked teeth that it uses to munch on crustaceans, smaller fish, molluscs and seabirds.

The duel to the death between a shark and an orca (video)
There are those who play with sharks: don't you believe it? Look here!

This nymph - or larva - of dragonfly (Anisoptera sub-lines), seems to smile satisfied in an enlarged photo.

Only when it is ready to "mature" will the little one emerge from the water, breathe deeply (and no longer with the gills) and, attached to a branch or a rock, will free itself from its larval exoskeleton, to take on features and colors of an adult dragonfly.

Try to recognize another notorious insect from its larva

An Israeli gentleman presents his Carlino, Ghandi, in a competition in which the similarity between the dog and his human "friend" is evaluated. Will they have won? Who knows. The smile is actually the same …

Dogs to the rescue: the most beautiful photos of Fido

Diving dogs: spectacular shots

Other moving examples of friendship between man and animals

Despite appearances this barred owl (Strix varia) is not smiling at all: it is yawning.

Find out why they say "be silly like an owl"

Flying with the fastest raptors in the world: go to the video

It is not a photomontage. This squid "smiles" indeed: to make the animal - a specimen of Helicocranchia pfefferi as big as an orange - so cheerful, so to speak, is a strip of colored pigments arranged in the shape of a smile.

About the habits of the "suckling" squid, named for the rounded shape and the funny tuft of tentacles, not much is known yet. According to the experts of the Cabrillo Marine Aquarium in San Pedro (California) where it is kept, it is not a great swimmer and wanders through the ocean floor at more than 100 meters of depth, shedding light with two bioluminescent organs placed behind the eyes.

The funniest of the abyss! The photos

Other fascinating sea creatures in this gallery
Photo: © Gary Florin, Cabrillo Marine Aquarium

A camel (or dromedary, given the back is not seen) shows its teeth in a moment of pause at a water source near the town of Aleg, in Mauritania.

Don't miss the gallery dedicated to the teeth of the animal world

Curious pattern in the shape of a smiling face photographed on the surface of a living coral of the species Montastraea faveolata. These endemic organisms of the Caribbean, the Gulf of Mexico, Florida and the Bahamas, are classified as "in danger" in the IUCN list: in the last 30 years its specimens have decreased by 50% due to diseases and bleaching, the whitening of corals due mainly due to the increase in water temperature.

This carefree ladybug seems to smile as it settles on a mushroom. To portray her with such precision was the Dutch Leon Baas, specialized in macro photography. Thanks to special lenses and lenses, Baas captures the movements of ants, beetles, crickets and snails without missing a single detail.

And speaking of insects, look at them very closely in this gallery
The funniest and craziest insects in circulation: the photos

It looks like a smile but it's a dentist's session. Underneath the drills and tongs a horse has finished this time. We are in Colombia and this is not such a strange thing: to supplement your salary, dentists often offer their services to horses used in horse-riding competitions. The proposed treatments, which also include the creation of molds and equipment to correct any problems with tooth alignment and bite, are usually performed twice a month over a six-month period, for a cost per session of $ 170 ( just under 130 euros).

To know everything but everything about horses look here.

The teeth on display, together with the backward-facing ears, indicate that this zebra was scared. Perhaps from the photographer.

A badger (Meles meles) smiles happily, and he is not wrong: he was saved from a flood that hit the immense floodplain of the Pantanal, in Bolivia. The teeth of this animal are well adapted to an omnivorous diet: in addition to the meat of worms, rats, moles and insects, these mammals also like fruit, cereals, tubers and occasionally mushrooms.

The face of this dragonfly (Aeshna cyanea) is definitely funny.

The Aeshnidae family groups the strongest dragonflies of the entire Order that live all over the world alongside tinned water, in marshy areas, along paths and hedges but also in the city. The females lay their eggs in small groups, within cuts made in the vegetation.

A gray seal (Halichoerus grypus) lying on the sand of Helgoland, Germany. It seems that the animal is rolling with laughter, but in reality its expression is caused by the typical shape of the muzzle.

These seals are also called "hooked-nose sea pigs", due to their size: an adult male can weigh up to 350 kilos.

If two horses, one male and one female, show each other their teeth, they are probably demonstrating willingness to mate. But if a specimen brings back its ears, lowers it, and shows its teeth, it is a sign of growing nervousness: better to stay away from it, if you don't want to fix a bite.

Don't miss the gallery dedicated to horses

Do not be fooled by that sympathetic air, this peacock canis (Odontodactylus scyllarus) hidden on the depths of Bali, Indonesia, is a cruel huntress. Once the prey has been conquered - crabs and other small crustaceans - it takes it "to barrel" with the legs to break the shell and eat the meat.

With the same violence, in some cases it can even break the glass of the aquariums!

Also read: the "left" killer of the peacock canocchia

This donkey (Equus asinus) smiles peacefully, photographed behind a fence in Missouri (USA). Thanks to their sociable and open nature these animals are often flanked by weaned foals and all those injured, nervous or recovering farm animals. It is said that the presence of the donkey has a calming effect and helps other individuals to deal with stressful situations (for the same reason these mammals are increasingly used in therapy with disabled children).

More than a smile, that of this dog seems like a real laugh. And if the expression of happiness of a dog is read above all by other physical signals, such as the movement of the tail, according to the experts even among the dogs one can distinguish the optimists and the pessimists (go to the news).

Do you understand what your dog says? Find out with this multimedia

Do you want to know what Fido is thinking? The fMRI tells you

The smile highlights the teeth of this domestic goat (Capra hircus). Thanks to a remarkable ability to select the foods and the edible parts of the same plant, in addition to the good adaptation to fibrous forages, the goat is also bred in places where there is not a large availability of food and greenery.

Did you know that even goats learn an accent?

How do goats climb trees?

I wonder what this cat is thinking about that seems to be laughing through the vibrissae.

He may have admired the exploits of Dusty, the kleptomaniac cat or this other cat who likes to burst soap bubbles.

More beautiful pictures of cats in this gallery

Do you think you know every habit of your cat? A test to find out

It is easier to see a hippopotamus (Hippopotamus amphibius) "smile" - or rather, it is easier to see it quiet - in winter, when the weather conditions allow it to spend most of the day resting in the water. In the dry season, instead, when the resources are scarcer and the predators more numerous, it often happens to see these bestioni show defensive behaviors as yawns, repeated beats of the jaws and bites.

The fight of the hippos: watch the video

The placid and sly expression of a frog.

All the most curious and funny frogs in this gallery

The mysterious smile of the Philippine tarsier (Tarsius Syrichta) is due to the particular shape of the mouth, suitable for containing small sharp teeth. Add two eyes that are disproportionate and fixed in the orbit and the portrait of the curious primate is accomplished.

See also the tarsier that resembles Master Yoda

Between the sinister sneer of his teeth and a graceful "hairstyle" of butterflies, this caiman from Paraguay (Caiman yacare) seems to have posed for a photo.

Fortunately for the reptile it is not greedy of lepidoptera, but of river lumacone and freshwater fish, delicacies obtained with the most imaginative hunting techniques. Some ethologists have observed him behaving like a "dam", and gather the prey with which he barred the road. Greedy of piranha fish, this beast (even 3 meters long) is often nicknamed "caiman Piranha", perhaps also due to the disquieting teeth it shows off.

Caimans, crocodiles, lizards … don't miss the gallery dedicated to reptiles

To be able to lick one eye with the tip of the tongue, this Henkel "leaf tail" gecko gave us the most radiant of his smiles.

Can you distinguish another gecko, this time mimetic? Look

A subspecies of parrot fish, the "semaphore" parrot fish (Sparisoma viride) shows off its big teeth. This fish typical of the Caribbean seabed has the particularity of changing sex - and colors - during its life: it is born male or female, but in the second phase of existence it is always male. The nickname "traffic light" comes from a yellow spot near the pectoral fin that makes it immediately recognizable.

Yakini, a little gorilla newborn at the Melbourne zoo (Australia) first gets scared by the cold of the stethoscope and then seems to enjoy the relief of not having it on his skin anymore.

You might also like: 15 incredible photos of mammals Nature takes life Friends beasts We could only open with the self-timer of a particularly enterprising specimen of a Sulawesi crested black macaque (Macaca nigra) who made a series of photos of his smiling big face while she fiddled with the equipment of an English photographer, in the north of Indonesia.
The initial distrust of the equipment soon gave way to curiosity: "Before I could recover my camera, the group of macaques had made hundreds of shots, " explained the photographer. "At first they took a lot of pictures of teeth, " he said, "although most of the shots came out of focus" (look at two more photos of the episode).