It’s easy to recognize a rattlesnake by the rattle at the end of its tail.  The rattle is a series of horny, cup-shaped rings that fit loosely into one another.  When a rattlesnake rattles, it is usually because it has become alarmed.

This makes it vibrate its tail rapidly.  The hollow rings strike together and make  a sharp buzzing sound.

By making its rattling noises, the rattlesnake is able to warn away bigger animals that might step on it or harm it.  Although a rattlesnake often gives a warning before it strikes it may also strike without rattling.–Dick Rogers