A common response with doms I'm friends with to "I'll do anything you want" or "I have no limits" is to ask which finger they want to lose. They don't actually do anything, but it's a way of teaching that there are absolutely things you don't want done to you that other people may want to do to someone and you really need to learn to convey at least the basics of what you want and don't want both for your safety and to avoid making the dom do all the work of figuring out the scope of the scene.

Well, you see, "anything" is very broad and could include removal of a finger or two. Specificity is good when defining boundaries.