Pizzicato
When instruments of the violin family are played pizzicato the player usually plucks the string with the index finger (pointing finger) of the right hand somewhere over the fingerboard. Bassists typically use the index and middle finger. Sometimes the player may rest the thumb on the edge of the fingerboard to keep the hand steady. Sometimes more fingers can be used for particularly fast pizzicato sections.  Cellists and double bass players can use the thumb for plucking, especially for playing chords.