Reptiles are fascinating and intriguing creatures found on every continent of the world other than Antarctica. They are present globally, nationally, and locally. Individuals often find themselves unfamiliar with local reptiles. The wide spread consequences of ignorance regarding these organisms means that in todays society, local reptiles are feared and reviled. They are considered to be slimy and disgusting creatures. While some reptiles can be poisonous, such as the Gila monster (Heloderma suspectum), the beaded lizard (Heloderma horridum), and various rattlesnakes, vipers, and adders, the chemical and mechanical defenses of most reptiles lack enough potency to kill human beings and have evolved to kill only a specific species of prey such as voles, mice, and birds. Disregarding the poisonous reptiles mentioned previously and potentially dangerous creatures such as alligators and crocodiles, many local reptiles such as lizards are harmless and even make good pets. Additionally, there are many more species of non-venomous snakes in the world compared to the numbers of species of venomous snakes. Furthermore, the skins of local reptiles are not slimy but instead covered with scales, or a layer of hardened epidermis, and are cool to the touch. This is because reptiles are cold-blooded animals that lay eggs, known as oviparity. Unlike mammals, whose body temperature does not vary as the result of environmental temperature changes, cold-blooded organisms need to manually regulate their body temperature through sunlight exposure, or basking. All local reptiles use lungs to take in oxygen, though there is a species of turtle with semi-permeable skin that allows the turtles to increase oxygen intake while in water. Turtles are the only local reptiles with calcium carbonate shells. These shells allow them to retreat inside in order to protect their heads and limbs at any hint of danger. All local reptiles are vertebrates with hollow nerve cords.