People are just kidding when they say they would give their eyeteeth or right arm for something. It's a way of saying you really, really want something. But no one is going to give away one of those necessary body parts!
Speaking of eyeteeth, did you ever wonder how they got their name? It may be because the teeth are right below the eyes or because the nerves for these teeth are close to the eyes. Without eyeteeth, it would be pretty hard to tear into your favorite sandwich.