Many reptiles are have earned a reputation for being slow, but some -- like snakes and crocodiles -- can move extremely fast when threatened, or catching prey. Due to their cold blood, they must seek out sources of warmth (like a sun-warmed rock) to help balance their body temperature, and therefore tend to live in climates where it's warm all year round. Dry-skinned and scaley, most reptiles lay eggs just like birds. Eggs aren't the only thing they share in common with birds: many scientists believe that reptiles and birds are direct descendents of the dinosaurs.