Dolphins.
I was a programmer at a dolphin research project, and I also participated in the dolphin training. In between doing useful things, I played with the dolphins all day intermixed with the Calculus lessons.
One day my pen fell out of my pocket into the tank. One of the dolphins snatched it and swam out into the middle of the tank. This is a very bad thing because dolphins, brilliant Einstein intellects that they are, tend to be stupid about what things are okay to swallow.
I reached out over the water as far as I could, hoping to coax the dolphin to bring my pen back. Dolphin approached close enough to where I just barely couldn’t reach it, and sat there a while. When I tried to reach out for it, the dolphin tossed it back out toward the middle of the tank. Then swam out the the middle of the tank and got it.
Repeat.
Repeat again.
After that, I managed to snag it finally.
Now, do you think dolphins have a sense of humor?
One afternoon, after the training sessions, one of the trainers taught one of the dolphins to twirl a frisbee on the end of its snout. Apparently the dolphin thought this was a big kick, because that dolphin spent the rest of the afternoon and all night and most of the rest of the week, swimming around the tank, twirling a frisbee on its snout. By the next day, the other dolphin had picked it up too, and both of spent all their free time twirling frisbees. (Dolphins are extremely imitative.)
Then they got into the habit of putting the smaller frisbee inside the larger frisbee and twirling both of them at once.
We had to drill holes in all the frisbees, because the dolphins were fond of putting a frisbee over the drain so that the tank would overflow. Then they would swim around the outer edge of the tank at top speed, causing tsunami waves in the tank and flooding the surrounding deck.