I have just thought about the cat butt wiggle. In England we might call it “the cat bottom wiggle”. You don’t always see it. Some cats do it more than others and the cat in the video has variations on the theme.
I don’t recall seeing an explanation for this type of cat behaviour. The reason for it must be either physical or psychological (or perhaps both) and I have decided it is primarily a way to mentally prepare for a chase, attack or a pounce (on prey) because there is little physical benefit to it as far as I can see. However, there may be a physical element to it which is secondary. It may prime the muscles in the hind quarters in readiness for a explosive contraction which propels the cat forwards rapidly.
In respect of mental preparedness, I’m sure that there are many equivalent human forms of behaviour which are done the same reason. For example, when a person is about to embark on a difficult task employing considerable mental and physical exertion, sometimes he or she will take deep breaths or a single deep breath. Tennis players, bounce the ball before serving and golfers waggle the club before hitting a drive.
And so the domestic cat winds himself up mentally by wiggling his butt. He “girds his loins” (“to prepare [oneself] for action”1)to use an old-fashioned phrase.
What do you think 😉 ?
Note: (1) Free Dictionary definition.