Reptiles, being cold blooded, are dependent on the environment to provide sufficient heat. If they get cold, their metabolism can become so sluggish that they cannot defend themselves, not even against a mouse.
Careless owners of small snakes have been known to toss a live mouse in with the snake and then not supervise. If the snake is cold, the mouse can eat the snake alive and the snake cannot retaliate.
If the snake survives such an attack, it may have such a fear of mice that it will no longer eat. It can take a year of tube feeding before the snake gains the confidence to face another mouse.