[O]ther things being equal it is worse to cause an animal pain than to cause an adult human being pain. An adult human being can, as it were, think his or her way around the pain to what lies beyond it in the future; an animal -like a human baby-cannot do this, so that there is nothing for the animal but the pain itself.

Judith Jarvis Thomson, The Realm of Rights, Cambridge, Massachusetts, 1990, pp. 292-293