Historically, for example, sea-life rarely made it into humanity's realm of concern when it came to the ability to suffer. But meticulous experiments performed on trout a decade ago essentially have laid to rest the common view that a fish cannot feel pain. There now is also scientific support for sentience in at least some invertebrates. In research by Canadian biologist Jennifer Mather and colleagues, octopuses show curiosity, play and personality. And in a study led by Robert Elwood at Queens University Belfast, prawns spent more time grooming and rubbing a pinched antenna, unless they received a follow-up application of local anesthetic.
Once deemed inscrutable, animal emotions are now also considered a legitimate source of inquiry. Although humans cannot know for certain what an animal is feeling (indeed, we cannot know for certain what another human is feeling), we can observe changes in behavior and physiology and infer emotions. The evidence is even more compelling when we find that these changes echo changes in our bodies when we are exposed to similar stimuli.