You begin by fucking a girl doggystyle, than when shes not paying attention you stick a maraca in her ass, grab her hips, and pound away. This will cause the maraca to make the loud "rattle" nose resembling the sound of a rattlesnake.
The Rattlesnake can be described in the following situation. Billy fucks Sally doggystyle than inserts a maraca in her ass to cause the instrument to make a nose. Basically, Billy turned Sally into a 5 ft maraca of love.