Well, there's a lot of complexity in those codes. They're constantly changing, from week to week and even play to play, and some codes only mean something in combination with other codes, if that makes sense. And if an offensive coach or quarterback suspects that their opponents know what play is coming, they might call an "audible" — a new or substitute offensive play, announced via a different set of codes. (Yeah. It's complicated. Peyton Manning makes it even more complicated by occasionally calling plays in Gaelic — see the video above.)