The point in the middle of a movie when you take a nap. No one can watch an entire movie in one sitting so this is the nap in the middle that everyone takes.
No way we can finish this movie in one go. We have to have a middle nap, of course.
The theory that if you own a pair of pants, everything inside it is yours. If someone wears your pair of pants, all the things inside the pants at that time, including their butt, belong to the pants owner.
According to pants containment theory, you're borrowing my pants therefore that's my butt.