to keep a secret, mum's the word
Não diga a ela que o chefe vai demiti-la, boca de siri!
Don't tell her that the boss is going to fire her, keep it a secret!
The expression boca de siri ("crab's mouth") draws on the anatomy of the siri, a small crab whose mouth is so tiny it is hard to see with the naked eye. The crab grips its prey and barely lets go, keeping that minute mouth shut even after death.
Source: Conservando Valor.
Falando's Idiom Trainer teaches you to recognize idiom meanings and create sentences using them, so you can speak like a Brazilian.
