Our cat Elsa needs lots of entertainment. In our last attempt to make her happy, we bought her a Flippity Fish: a plush that looks like a fish, but it starts wiggling and flipping when its body gets hit.
It looks really nice and fun, but Elsa disagrees. When it starts moving, she immediately leaves it and looks at it from a distance. I think she's scared of how much and how long it moves. To prove my theory, I took it apart and looked for ways to reduce the wiggling, or even make it remote-controllable.