When it is alarmed, it rattles its tail to frighten off the intruder. The snake's rattle is made of hard sections of old skin. A new one is added each time the snake sheds it skin. The sections fit loosely over each other in an interlocking series. Once the snake is fully mature its rattle does not change size.
Older segments drop off at the same rate as the new ones develop.
One species of rattlesnake on Catalina Island off the coast of California has no rattle. The longer the snake's rattle, the quieter is its sound. More people are bitten by diamondback rattlesnakes than any other North American poisonous snake. But the Mojave rattlesnake is 20 times more lethal. More people in the United States die each year from lightning strikes than from snake bites.