молчать (помалкивать) /помолчать в трйпочку highly collVPsubj: humanmore often impfvoften imperfixedWO
to keep quiet, not express one's opinions, views, ideas aloud
X молчит в тряпочку — X keeps his mouth (his trap, his yap) shut
X keeps mum.
Обыкновенные люди к этому времени уже научились молчать в тряпочку, и шумели только старухи в очередях (Мандельштам 2). By that time ordinary people had learned to keep their mouths shut, and the only ones who still made any fuss were old women standing in queues (2a).