The bigger bulge, the better
for all you faggots that never got laid;
i do this all the time with my girlfriend, since you hit the G-Spot really good if you do it.. My girlfriend loves it, she started to squirt like crazy!
As someone of the female variety this is totally a thing. It actually depends on the girl though. Smaller girls its easier to see but this happens it all girls... It's literally how it works. Some girls have different shapes though so it's gonna be a bit different depends on the girl. I for instance have really wide hips so unless I'm laying on my back with my back arched its not noticeable. But one of my girlfriends had a really slight build and smaller hips so you could kinda see it regardless.
if you read the tool tip (hover mouse over it; iPhone probably can't do this) it'll say: "skinny red-faced girl Sammie Daniels with abdominal distensions from being fucked 89091.webm"
Dunno if that'll lead to sauce but it's a lot more info
Here is a shitty shoop, sadly never saw the original anywhere.