Usually happens with the woman on top, especially if she is of substantial size.
Riddle/Joke?
What can a bird do that a man can’t, besides fly?
Two large bulls and a small bull watched a huge bull being unloaded off a trailer. One big bull said “I’m going to mosey down there and give him half of my herd.”
The other big bull said “I’m going to do that, too.”
The little bull started snorting and pawing the ground. The big bulls asked him “What the heck are you doing?”
The little bull said “I want to make sure he knows I’m a bull.”