u can also hold wooden dowel behind neck and pull tail to seperate spinal colum. this should only be done carefully because the skin can come off the tail and cause the rat alot of pain. then u could also do the one hit skull method but makes bloody mess
I worked in an animal lab for years. Here's the "How to" of hit-'em-on-the-head, which is without a doubt the most merciful for the rat, (C02 being only merciful for the human observer...)
1. If rat is tame, hold it on your left hand with its head looking over the back of your hand, front paws on top of your hand, back paws and tail hanging.
(- if rat is not tame you can quieten it down considerably by hanging it by its tail and spinning it a few times by twirling the tail between your fingers so it gets dizzy)
2. Hold tail in your right hand.
3. Stand in front of a hard surface such as kitchen or bathroom counter
4. Swing back of rat's head FIRMLY and without hesitation against hard surface to stun it. Once should do.
5. Place stunned rat quickly belly down on hard surface
6. Place something solid but not sharp (such as the edge of a wooden kitchen spatula, or as you say wooden dowel or sp0on handle) immediately behind the rat's skull.
7. Pull on the tail, not just backwards but also angled upwards about 45 degrees
8. You will feel the neck give way - it does not have to be hard (certainly not hard enough to have the tail skin come off, although it happens sometimes with mice)
9. Rat is now effectively dead. It will kick but this is reflex nerve action, not a concious struggle.
HIGHLY RECOMMENDED - buy a few frozen rats and practice with dead ones before you go on to live. This is only kind when it is done with certainty and confidence.