Hedgehogs are the only rodents that roll into a ball when in danger. This is a way to protect them from predators, but it also stops them from rolling out of the ball. The majority of species are small enough to fit in an adult's hand. They range in size from four to twelve inches, and weigh between five and 56 grams. They can also be purchased online. It is important to remember that they are not available for purchase after they have been born.