http://en.wikipedia.org/wiki/Wood_block
http://www.curriculumonline.ie/en/Primary_School_Curriculum/Arts_Education/Music/Music_Teacher_Guidelines/Appendix/How_to_hold_and_play_some_percussion_instruments/How_to_hold_and_play_some_percussion_instruments.html?print=1
The wood block, or two-tone wood block, is a percussion instrument that creates sound when hit together due to a resonating chamber.
Two-Tone Wood Block
As the name suggests, this instrument can produce two different tones.
It is held by the handle and each side is struck with a wooden beater.
The Paul Laurence Dunbar High School Percussion in 2006
performing visual drumming using woodblocks and black light.