Meaning
All hell is going to break loose
Example
Agora que a justiça o obrigou a assumir o filho, a cobra vai fumar!
Now that justice forced him to take responsibility, all hell is going to break loose!
Origin
The phrase a cobra vai fumar ("the snake is going to smoke") was born in World War II. When Brazil was slow to join the fighting, skeptics joked that it was "more likely for a snake to smoke a pipe than for Brazil to go to war." The Brazilian Expeditionary Force turned the taunt around, adopting a pipe-smoking snake as its emblem and calling its soldiers the Cobras Fumantes ("Smoking Snakes").
Source: Aventuras na História.
Practice idioms with the Idiom Trainer
Falando's Idiom Trainer teaches you to recognize idiom meanings and create sentences using them, so you can speak like a Brazilian.
More idioms
Acertar na moscaTo guess correctly / To hit the nail on the headAmigo da onçaA fake/false friendAndar na linhaTo toe the line / To behave properlyArmar um barracoTo cause a public sceneRodar a baianaTo cause a public scene / To go ballisticArrumar sarna pra se coçarTo ask for troubleArrastar as asasTo hit on someone / To flirtAbrir o jogoTo come clean / To open upArregaçar as mangasTo roll up one's sleeves / To get to workAgarrar com unhas e dentesTo hold on for dear life / To seize an opportunity