Well, I expect that humans and animals feel the same amount of pain/discomfort, at least. When I accidentally step on my 75-pound dog’s foot, it probably hurts about the same as when he steps on mine (except that I don’t also have claws digging in). When my cat had pancreatitis, she didn’t budge from one spot in the middle of the hall all day because she felt so horrible and moving just made it worse. But then again, they may not attach emotion to it like we do, which may have an impact. But they have nerves just like ours, and their brains are just as able to detect pain, I would think - it’s something they’d need in the wild, so their brains would tell them, say, “My leg hurts, so I should stay off it for now,” which would lead to them giving the injured leg a rest and allow it to heal more quickly.
The reaction will also be different if it is not a social animal, which may make it look like the animal isn’t suffering as much whether it is or not. A social animal like a human has the instinct to make noise and attract attention from members of its species for assistance if injured, whereas a non-social animal’s instinct is to find somewhere to hide and make as little noise as possible to avoid drawing predators.
It just seems to me that the reaction to pain would be just as beneficial to a wild animal as it would be to a human, so it makes sense that nature would have selected for it in them, as well. (Can you tell I majored in biology? )
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Yet in my new wildness and freedom I almost welcome the bitterness of alienage. For although nepenthe has calmed me, I know always that I am an outsider; a stranger in this century and among those who are still men.
-H. P. Lovecraft, "The Outsider"