Why don't animals hate?

I saw an interesting story on National Geographic channel once. A group of migrating elephants was passing a river or something with crocodiles in it. A young elephant wandered into the water, away from the herd and was killed. When the elephants migrated back that way a decade later, they picked the crocodiles up with their trunks and beat them against the trees for hours, long after they were dead. Guess the old saying about an elephant's memory is true