As noted... when a snake kills its prey it is far more efficient that what you did.
You may love your snake, but if you are going to kill your own prey then you need to respect and honor the prey as well.
Snakes are efficient at what they do... what you did was not. Maybe that is not what you want to hear, but the reality is that you need to educate yourself regarding humanely euthanizing your feeders.
If you are feeding one animal to keep another alive then you need to respect both of them. Do not be glib about it, and pay homage to what that rat is "giving" you and your snake.
There is plenty of information available that addresses how you can do this humanely... read humanly... and it is your responsibility to take that seriously.
Bruce