The term cold blooded refers to the fact that reptiles do not have the internal mechanism to regulate their body temperature to one that will allow their bodies to function effectively. Mammals and birds can do this but the cost is high, about two thirds of the energy produced from the food they eat is used to maintain a suitable body temperature. Reptiles must find a warm place for basking to raise their body heat and some cooler spot to move to from time to time to prevent overheating. This means they must spend some time lying in the open and exposed, especially the smaller ones, to possible predators. To protect themselves against this most reptiles are able to blend in with their surroundings and by keeping quite still can be hard to detect.