don't run the car for very long. once the thermostat opens, hot coolant runs through the heater core, which would be bad if the snake was near it. Do not run the blower fan for heating and cooling. incase the snake made his way in there. Honestly I would be taking my dash apart, but I've been working on cars my whole life. If your car is factory, it is doubtful they would have a way out of the car. but there are 12904833902 models of cars and obviously I can't say that for sure. If you have a garage you can clear out or something, pull in there to get out of the cold weather or better yet push it in there. maybe a heat pad under a hide on the floor board might get their attention? but basically your snake is scared and they aren't going to want to come out.

future advise, either use a snake bag/pillow case to transport them in or something like like this with a few holes in it. http://www.sterilite.com/SelectProdu...=253&section=1

also... suspected rat attack?