Vibrato is a technique that creates an oscillation of sound, starting on one pitch, dipping slightly below the pitch, and then back up to the true pitch. It is used to create expression in the sound of the violin. There are two ways to physically do vibrato, starting from the wrist and starting from the arm. Wrist vibrato involves rocking the finger from tip to pad. Arm vibrato involves opening up the arm and elbow joint to allow the arm to pull the finger in a motion similar to the wrist method. Either method is perfectly acceptable, although many teachers will start a student with wrist vibrato and then add arm vibrato later.