Clouer le bec à quelqu’un, “to shut someone up”, usually means the person won an argument, leaving the opponent speechless. In this expression, clouer has nothing to do with the homophone verb clouer, “to nail”. It comes from cloer, “to close”. So how about le bec (“beak” in English)? Well, it is a slang word for the mouth and is used in a lot of idiomatic expressions in French. From there, clouer le bec is an expression easy to understand!