At our zoo trip, most of the time the kids wanted to go see an animal, watch it for, oh, about 10 seconds, and then move on. For a lot of animals I don't mind too much but I am extremely fond of the big cats, and when the big cats are active I can watch for hours.
My camera was especially happy with the amur leopard, because I was photographing through relatively clean glass rather than those obnoxious wire fence nets. Also I had brought a decent zoom with me. So we stayed a little while to admire.