It did not happen in a zoo, but here it goes:
Today, I was out for a walk with a "mate" of mine. Suddenly he picks up a frog (common frog), flings it in the air and tries to kick it. He misses, but still it falls down and is dead. When asked why the HELL he did this to an innocent animal that he did not even have anything against, he replied: "Because it's funny". I can sort of understand that you kill a spider if you are afraid of them, but why kill a random frog that has not bothered you the least - and they are even protected in Denmark, so I could actually have turned him in to the police, but I think that is overdoing it, and the police probably would not bother. Nonetheless, I felt like hitting him at the side of the head, but I restrained myself because I do not like violence and I would not be better than him, then.