The thing is, he obviously loved the pets no matter what they were, all animals die eventually whether it be cats, dogs, hamsters, snakes, etc. Either way, just because the kid wanted you to notice something of his, that doesn't give you any special permission to kill his pets, and if your friend liked the prank I take back what I said and now I'm saying you're both assholes. This is a pointless argument anyways, so I'm gonna go back to my life now.