What's inside a rattlesnake's tail?

If you look inside a rattlesnake rattle, you’ll find it’s actually hollow. Instead of shaking loose bits like a maraca to make that famous sound, rattlesnakes clack together segments of keratin — the same material found in your fingernails. They use three shaker muscles to vibrate the tips of their tails up to 90 times a second, which is many times faster than you can blink!