Fun facts that kids want to know and love to share, including how many muscles, how much hair, the hourly breath count, and the heartbeats per day. National Geographic supports K-12 educators with ELA Common Core Resources. Visit www.natgeoed.org/commoncore for more information.About the Author: Robyn O'Sullivan is the author of several National Geographic History and Science Chapters, including Jackie Robinson Plays Ball, The Wright Brothers Fly, and Your 206 Bones, 32 Teeth, and Other Body Math.