In areas where cattle, sheep and goats are free to roam, bells may be used to identify those belonging to a particular herd and help trace their whereabouts when the herdsman needs to gather them in. They are commonly trapezoid, cylindrical or cup-shaped. These bells have been used in various musical contexts.
Greek herdsmen often use several bells attached to principal animals which produce a distinctive chord. The scale on which this chord is based is then reproduced in the herdsman's pipe - so he can play along with the herd! Similar bells have been used in Western European "Classical" music where a pastoral mood is invoked.
Clapperless cowbells made of metal are an important element in Latin-American music. These are struck with a stick - the tone being modulated by striking different parts of the bell and by damping with the hand holding the bell.
In several parts of the world (notably in West Africa) pairs or trios of clapperless bells are joined in such a way that they can be struck separately or clashed together. The Brasilian name for these is "agogo" bells. Cylindrical woodblocks played in the same way are also called "agogo". Many popular recordings have featured the cowbell, most notably War's Lowrider.
During a popular SNL sketch, Christopher Walken played a famous producer insisting that "More Cowbell" is the key to making Blue Oyster Cult's "Dont Fear the Reaper" a success.