Snakes are cold-blooded creatures, just like amphibians. When a certain animal is cold-blooded, it basically means that they are able to adapt their own internal temperature to that of their environment. When a snake is in a cool environment, their body temperature tends to drop rather quickly.
When one of these reptiles is in a warm environment, their body temperature rapidly increases. Although being cold-blooded certainly has its benefits for snakes and other creatures, if one of them is exposed to a cold environment for too long of a time, they will like lose consciousness and eventually die.