This is the animation assignment I just finished where I'm expected to put some secondary motion in a tail (secondary motion being movement of something that's loosely connected to the main subject). The bare minimum of the guidelines would require me to move a ball with a ribbon-like tail around the screen in the cardinal directions, at different speeds, etc. But would that be fun?

No. Squirrels are fun. Look at this squirrel. It's a million times better than a ball at least. And I guarantee that if I was just sticking to the ball I would have no fun doing this at all.

So to review, squirrel = fun > not fun = stupid ball.