Noun: A flexatone is a small percussion instrument consisting of a tapered sheet of flexible metal mounted in a wire frame. When the frame is shaken, the blade is struck alternately by two balls attached at the end of springy metal strips on either side of the sheet, and the pitch can be changed by varying pressure on the blade.
The flexatone is a modern creation originating in about 1922, initially used as a special effect in jazz and a few early 20th century orchcestral pieces. It later became popular in the 1970s in funk and rock. Nowadays, you might hear it as a spooky sound in cartoon and film scores.