According to Hutchinson, butt-wiggling may help press the hindlimbs into the ground to give cats added friction (traction) for pushing them forward in the pounce. ... "And we can't exclude that it's just fun for cats; they do it because they are excited by the thrill of the hunt [and] prey."

Why does my cat wiggle before attacking?

“When a cat wants to pounce on something, they wiggle their hind ends back and forth to check their balance. It helps them determine if they have solid ground under their hind legs to pounce and also helps them determine if they will make the jump distance safely.

How do you tell if a cat is going to pounce?

Quickly turning his head toward a person's hand. Twitching or flipping his tail. Flattening his ears or rotating them forward and back.