to spill the beans, to let the cat out of the bag
Pedi para não contar nada, mas ela deu com a língua nos dentes e todo mundo ficou sabendo.
I asked her not to say anything, but she spilled the beans and everyone found out.
The expression dar com a língua nos dentes ("to strike the tongue against the teeth") paints the very act of speaking: to form words the tongue beats against the teeth. It pictures a mouth that runs on without restraint, letting slip what should have stayed quiet — hence "to give away a secret".
Falando's Idiom Trainer teaches you to recognize idiom meanings and create sentences using them, so you can speak like a Brazilian.
