It's a small percussion instrument that is played with the help of mouth.
How it works?
It consists of a flexible blade stuck in one end to a metal frame or bamboo. The other end of the loose blade is pinched with the finger of the performer, and the instrument frame gets stuck in your teeth. By changing the shape of the mouth when holding the berimbau you can change the sounds produced, suggesting different musical notes.
A bit of history ...
The mouth berimbau is a very ancient instrument of Asian origin. It was widespread in Europe and came to Brazil still in the sixteenth century probably by the colonizers and Portuguese missionaries.
Apparently the instrument was very used in Rio de Janeiro in the eighteenth and nineteenth centuries, it was imported too often and in large quantities. Probably, at some point in the history of Brazil it has been considered just like a child's toy.