Call me slow if you already know this one but I just figured this out (all by myself) the other day. The sound you make when you fart, most of the time, is actually the sound of your left and right butt cheeks slapping against each other as air is passing through. I guess I discovered all this starting from the notion that you cannot clap with one hand, followed by the widely used practice of tilting ones ass to break wind discretely. You see, when you tilt your ass to one side, what you’re really doing is removing one butt cheek from the equation.