For those that are wondering about what the animal may be feeling in these situations. In my time in the military I was close to death on a number of occasions. Almost froze to death twice. Almost drown once. Freezing to death is not so bad. You fall asleep as your body temp drops. Drowning is far worse at the beginning as you fight the situation. Once your body is deprived of oxygen for awhile you begin to hallucinate and it is in its latter stages actually a peaceful experience.
When I have to kill a rat it is always by cervical dislocation. It is instant if you don't screw up.