(I’m eating a hamburger. I see the man next to me carefully picking a slab of cheese out of his burger, wrapping it in a paper napkin, and eating the rest of the burger. It puzzles me, so I ask him about it.)

Me: *point at napkin* “Excuse me, but why did you do that?”

Man: “Oh, every time I eat a burger, I set one ingredient aside. At the end of the week, I have a free burger!”