Quote Originally Posted by Medved View Post
Throbert, заткнись works in exactly the same way as shut up (yourself).
Medved -- I've been told that замолчи = "shut up!", while заткнись is more like "shut the HELL up, dammit!", and perhaps also has the connotation "...или тебе покажу, где раки зимуют."

In other words, same meaning, but stronger!