Put a Sock in It

A popular story claims this comes from early gramophones, which projected sound through a large horn with no volume control, and that stuffing a balled-up sock into the horn was the simplest way to muffle an unwanted record. It's a charming, very specific image, which is probably exactly why it's stuck around, but it's now generally regarded as a later invented explanation. The real origin appears to be First World War military slang, most likely Australian in origin, for telling someone to stop talking, plausibly evoking stuffing an actual sock into a noisy sleeper's mouth in a shared barracks. Both Britain and Australia picked up the civilian phrase around the same time, in 1919, carried home by returning soldiers.