One of the most complex mechanical features of the hurdy-gurdy is the 'chien' (dog), or buzzing bridge. This is a small, loose-fitting bridge that supports one of the drone strings. When the player turns the crank at a steady speed, the drone string produces a constant pitch. However, if the player gives the crank a sudden, sharp acceleration (a technique called a 'coup'), the bridge vibrates against the soundboard, creating a rhythmic buzzing sound. This allows the hurdy-gurdy player to provide their own percussion while playing a melody. This is a unique example of a stringed instrument being used to create a purely percussive, rhythmic accompaniment without the use of a separate drum. Mastering the 'coup' is the hallmark of a skilled hurdy-gurdy player and is essential for traditional French folk dance music.