Anger Quotes - page 19
Tis evident, that sympathy, or the communication of passions, takes place among animals, no less than among men. Fear, anger, courage and other affections are frequently communicated from one animal to another [...] And 'tis remarkable, that tho' almost all animals use in play the same member, and nearly the same action as in fighting; a lion, a tyger, a cat their paws; an ox his homs; a dog his teeth; a horse his heels: Yet they most carefully avoid harming their companion, even tho' they have nothing to fear from his resentment; which is an evident proof of the sense brutes have of each other's pain and pleasure.
David Hume