query: What is the rattle of a rattlesnake made of?
passage: Rattlesnake
The rattle is composed of a series of hollow, interlocked segments made of keratin, which are created by modifying the scales that cover the tip of the tail. The contraction of special "shaker" muscles in the tail causes these segments to vibrate against one another, making the rattling noise (which is amplified because the segments are hollow) in a behavior known as tail vibration.[1][38][39] The muscles that cause the rattle to shake are some of the fastest known, firing 50 times per second on average, sustained for up to three hours.[40]
passage: Crotalus catalinensis
Its most distinctive feature is its lack of a rattle. The base of the tail, the "button", has degenerated to such an extent that the rattle immediately falls off with each shed instead of forming a new segment, as it does in other species of rattlesnakes. This is widely believed to be a localized adaptation for hunting birds.