Not only cats but dogs also do same. Especially Japanese Shiba dogs with his curling tail.
Some bugs as well, ones stretch, shrink and crawl.
Cat stretch helps you comfortably stretch your back and belly,
Even though your belly droops, this exercise expand your belly vertically and tighten.
Same as other yoga poses, please stop and hold for a while when you reach to the point that you feel comfortable.
Firstly sit on your knees, lift your heels, gradually bend your upper body towards.
Breath in and out slowly, feel your body is stretching, check if there are any unstretched parts, then stretch more.
Then slowly release and come back.
How about pretending a cat?