How would I "euathnize a rat fuzzy/pup

[Beardedragon]

why cant you co2 a fuzzie until its 14 days old?

I would never just place a warm blodded animal in the freezer no matter how old they are.

Co2ing will not effect a mouse or rat under 14 days, I believe it causes acid to form it their lungs? Freezing would be the best way to do it henceforth.