A rattlesnake emits its famous warning signal without anything at all rattling around inside its tail. Here's how it works.

• If you opened up a rattlesnake's rattle, nothing will spill out. That's because it doesn't work like a maraca to make that distinctive sound-instead, the outer shell of the rattle, which is made of keratin, clicks together.
• The snake uses special shaker muscles to vibrate the tip of its tail up to 90 times a second. That's many times faster than you can blink!
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Following is a transcript of the video.

Narrator: If you're hiking pretty much anywhere in the US, this is one sound you don't want to hear... [Audio of rattlesnake rattle.]

The warning of a rattlesnake.

Now, just because a rattlesnake's tail sounds like a built-in maraca doesn't mean it works like one. There are no beads rattling about in here. So what's really going on inside?

If you opened up a rattlesnake's rattle and shook it, absolutely nothing would fall out. After all...

Colston: Rattlesnake rattles are hollow.

Narrator: That's herpetologist Tim Colston. He says the secret to that rattling sound comes from the shell itself. It's made of keratin, the same hard substance as your fingernails.

The keratin is arranged in a chain of interlocking rings, which are hooked together by tiny grooves along their edge. Now, watch what happens to those rings when Colston shakes the rattle.

Colston: Whenever I shake them really fast, they bump together, producing a sound.

Narrator: Because the rattle is hollow inside, sound waves can bounce off the walls and echo - the same way shouting in a cave amplifies the sound. And the bigger the "cave," or hollow rings in this case, the more amplification, so the louder the rattle.

But a big, hollow chamber can't get the job done on its own. That's where the tail muscles come in. Rattlesnakes are equipped with three powerful shaker muscles at the base of their spine. These can contract so fast, they vibrate the rattle up to 90 times a second!

For comparison, the human eye blinks 15 to 20 times a MINUTE! By vibrating so quickly, the rattle makes a sound that hits a specific frequency: 489 to 24,380 hertz. And it just so happens that range is best heard by mammals. It turns out that tail is custom-designed to make predators like bears, raccoons, and weasels LISTEN UP.

Unfortunately, snakelets - yes, that's what baby snakes are called - don't have this warning signal.

Colston: When a rattlesnake is born, it just has a single button that looks similar to this one [points to rattle], if you can see this part on the end here.

Narrator: Without a second button to clack against, the baby rattle can't make any noise! But every time they shed their skin, they add another button to the base of the rattle, which grows INTO the segment above. Sort of like the structure of a Russian stacking doll.

The rattle will keep growing until... SNAP. Just like your fingernails, those rattles are pretty fragile and can break off if they get too long. In fact, the rattles rarely make it past eight to 10 rings before snapping off. Luckily, snakes shed their entire lives. So the rattle will grow back, good as new.

Which is good news for you hikers. Because that handy tail can mean the difference between an exciting day on the trail and a painful trip to the hospital.