Castanet, First Chair
From the Super Mario Wiki, the Mario encyclopedia
The player must hold the Wii Remote in one hand and tap the top of it with the other hand to the beat. They must watch the rhythm of the bouncing notes as they approach the instrument and tap the notes as they pass. The notes turn into frogs as they pass over the trap; if a note is not properly tapped, the note(s) may be eaten by a snake.