Abstract This paper discusses a phenomenon familiar to many language acquirers, an involuntary rehearsal of second language words, sounds, and phrases. Current second language acquisition theory as well as case history reports of the “din” are consistent with the hypothesis that the din in the head is a result of stimulation of the language acquisition device, and is “set off” when the acquirer receives significant amounts of comprehensible input. The din may have practical value; it may tell us when we are providing input for real language acquisition in our classes.