[T]here is something odd about maintaining that pain and suffering are morally significant when felt by a human but not when felt by an animal. If a child burns a hamster alive, it seems quite incredibile to maintain that what is wrong with this act has nothing essentially to do with the pain and usffering the hamster feels. To maintain that the act was wrong because it might encourage the chid to burn other children or encourage anti-social behaviour, because the act failed to exhibit this or that virtue or violated some duty to be kind to animals—to hold these views seems almost perverse, if they are taken to imply that the hamster’s pain and suffering are no central data bearing upon the morality of what was done to it. For us, pain and suffering are moral-bearing characteristics, so that, whether one burns the child or the child burns the hamster, the moralità of what is done is determined at least in part by the pain and suffering the creature in question undergoes. Singer’s utilitarianism picks this feature up quite nicely, and it seems to me exactly right. Of course, there may be other moral-beraing characteristics that apply in the case, but the fact in no way enables us to ignore, morally, the hamster’s pains.
R. G. Frey, ‘Animals’, in Hugh LaFollette (ed.), The Oxford Handbook of Practical Ethics, Oxford, 2003, p. 170