The hedgehog's back is made up of two large muscles, which control the positioning of its quills. There are about 5,000 to 6,500 quills on the average hedgehog, and these are durable on the outside, while being filled with air pockets on the inside. The hedgehog uses its quills to protect itself from predators, using muscles which draw their quilled skin to cover their full body, and pulling in the parts of their bodies not covered, such as their head, feet, and belly. This form of defense is the hedgehog's most successful, but is usually their last resort. Hedgehogs are fairly vocal and communicate through a combination of grunts, snuffles and/or squeals, depending on species.
Hedgehogs are born blind. The hedgehogs are birthed with a protective membrane covering their quills, which dries and shrinks over the next several hours. The infants are born with quills beneath the skin, like pimples, and pass the skin after they have been cleaned.