Cat Belly Flap. If your cat is overweight, his belly fat does not move when he walks or runs. That loose flap of skin and fat on his belly is called the primordial pouch and it actually serves important functions.

What is the difference between the flap and belly fat? You watch as your cat walks away, and you see this belly flap swinging from side to side. It typically covers the length of a cat’s stomach but is most noticeable toward a cat’s hind legs.