What do rattlesnake tail segments produce when they are shaken?

Rattlesnake tail segments produce a warning rattle when they are shaken.

The rattle is made of interlocking keratin segments at the tip of the tail. Rapid tail vibration causes the loose segments to strike one another, producing the dry buzzing sound associated with rattlesnakes. New segments are added when the snake sheds its skin, but segments can break off, so counting them does not reliably reveal the snake’s age.

The rattle is primarily a defensive signal that can warn large animals, including humans, to keep their distance. It is not an indication that the snake is preparing to attack. A rattlesnake may also remain silent, especially if surprised or if environmental conditions make the sound difficult to produce or hear.

Rattlesnakes are pit vipers. In addition to the rattle, they use heat-sensitive facial pits and venom to hunt and defend themselves.