You can trust Sarah - she knows how to keep her mouth shut.Do you think I should keep my mouth shut about seeing Jim with another woman?
(sometimes + about)
keep (one's) mouth shut
To not discuss or mention something. He needs to keep his mouth shut and stop telling our family secrets to everyone in town!A: "It wasn't my fault. Brian said&mdash" B: "Keep your mouth shut, Chad!"
keep one's mouth shut (about someone or something)
Fig. to keep quiet about someone or something; to keep a secret about someone or something. They told me to keep my mouth shut about the boss or I'd be in big trouble.I think I'll keep my mouth shut.