The wiggle of the cat’s butt seems like an Mohammed Ali taunt. It’s like they are saying, “I’m gonna get you sucker.” When you play with your cat, perhaps dangling a mouse on a string, or when your cat plays with another cat, she may rear back, lowering her front and digging in her claws (if possible), and placing her weight on her hind legs, head low, butt high. Then, she wiggles her butt. You know she is about to pounce.
It’s cute, but knowing she’s a great hunter, we have to ask, why would she broadcast the pounce like this? Is she just being playful? Or is there a purpose to the butt wiggling?
Like most cat behaviors of this sort, we can only speculate.
One possible explanation is that it is related to how your cat sees. In order to execute a successful pounces, your cat needs to be able to judge the distance. Not quite leaping far enough would be a missed meal, and in the case of your feline buddy, a bit embarrassing if anyone is happens to be watching.
The problem is, as revealed in what cats see, a cat’s vision is not great close up and when they are closer to the object they are focusing on, their ability to judge distance is a bit compromised. Make no mistake, they are just as good as we are at judging distance, normally. But, when it comes to pouncing, they need to get it perfect.
So, the theory is that your cat is not really wiggling her butt, exactly, but shifting her weight from one back leg to the next which slightly shifts her head from side to side, which helps her judge the distance more precisely. If you watch the video below (maybe on mute), you can clearly see that when kitty wiggles her butt, her head moves from side to side.
As said, we do not know for sure whether this explanation is correct.
There may be other explanations for this behavior. Lest you think it is just a cute but purposeless behavior of the house cat, their big cat cousins do this as well!