Keep your mouth down

This is a great congruent conflation of “keep your mouth shut” and “keep it down”, both meaning to keep quiet.  “Keep” is the shared word that adds to the confusion.  It was heard on the movie “The Watch”.  Here’s the context (heroes talking to the skeptical police):

There’s aliens in the store.

Oh yeah? Aliens. Where?

It was right over there until you scared it. Now keep your mouth down.

http://www.subzin.com/quotes/M5919500d3/The+Watch/Now%2C+keep+your+mouth+down.

A big thanks to Barry Eigen for spotting this one and passing it on!