There's no pain at all with CO2 asphyxiation. You start them off slow, they pass out without being scared, then they're dead. You think being stuffed in a dark bag and being swung around and then being slammed into a wall is any less painless?
Fact remains that CO2 is approved by vet associations for being one of the only ways (cervical dislocation being another) to humanely euthanize a rat in the home.
This really isn't a hard concept to grasp, that CO2 is humane, and being slammed into the edge of a table is not.
