When we talk about physical pain, we all know how to bring it back to a precise feeling, vivid in memory. But how does a dog, a cat, a goldfish, a snake relate to painful stimuli?

The question is not trivial, because with animals - domestic or in freedom - we have to deal continuously, in a more or less direct way. Yet on this issue, illustrated in this video from the TED Ed series (in English, with subtitles), there are still many open questions.

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Two ways. When we talk about pain, we mainly refer to two types of reactions. The first is nociception: peripheral nerves come into contact with the painful stimulus, send signals to the spinal cord whose motor neurons activate muscle movements to escape the stimulus. It is an immediate and instinctive reaction, which guarantees our survival, and is common to almost all animals.

Awareness. The second reaction concerns the conscious recognition of that pain. In this case, the sensory neurons of the skin connect, through the spinal cord, to the brain. Here millions of neurons in various regions create a complex sensation that is often associated, in the case of man, with panic, stress and anxiety.

From what we can understand by observing them, many animals also live this second reaction: when they feel pain, they lick their wounds, they whine, they isolate themselves; they tend not to return to the place where they had that experience, as if they had a memory of pain. In the laboratory, rats and chickens self-administer painkillers, if specially trained.

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The sensitivity of the octopus. With invertebrates, which we know less, understanding if there is a consciousness of pain is much more difficult. In some cases where the nervous system is very elementary - such as for oysters and jellyfish - we can hypothesize no; in others, as with the octopus, awareness of pain could be even more complex than in vertebrates. These animals, in fact, know how to retract the wounded tentacles, to preserve them, but they choose to use them anyway to get food: as if they considered whether or not to use a broken limb.

On the subject of animal pain we still have a lot to learn, also to arrive at a man-animal relationship that does not cause pain for free.