Where the labia (womans lips :) ) hang low and create a flap.
I was watching a tv program where a woman had saggy lips, it reminded me of a cat flap.... And as another word for the vagina is pussy (cat) and people call the lips fanny flaps I put two n two togther.... VOILAAA! Cat flaps!!
"Get you cat flaps out!!l
The old lady bent over to reveal her cat flaps
The womans cat flaps whistled in the wind