Keratin makes up the segments of a rattlesnake’s rattle.
Keratin is a tough structural protein also found in human fingernails, hair, and the outer layers of skin. A rattlesnake’s rattle consists of interlocking hollow segments made from this material. When the snake vibrates the tail, the segments knock against one another and produce the characteristic buzzing sound.
A new segment is added whenever the snake sheds its skin, but old segments can break away. For that reason, counting the segments does not reliably reveal a rattlesnake’s age. The rattle also does not grow as a single solid object; it is a chain of loosely connected pieces.
Rattlesnakes use the sound as a warning signal, helping them avoid a close encounter. Not every rattlesnake rattles loudly, and newborns already possess a small button-like end even though they cannot yet produce the full mature sound. Rattlesnakes are pit vipers native to the Americas.