Key scene: Taking a weapon subconciously

(English movie, colour) I only remember this one scene, and its quite vague: Character A is talking, or focused on somthing else in quite relaxed way I suppose? The other character/s listen but are suddenly shocked and staring, and both Characters A and B (and maybe more) are confused. They all look at Character A and they say something like “Put it down,” in a very cautious and nervous way. Confused, Character B realizes hes picked up a weapon or knife without realizing it. The whole atmosphere is quite suspencful. Ring any bells?

Got something to say?