If you are looking to kill one at a time, I take them by the tail and wack them on an edge of a table or adjoining walls. I wack them once with enough force to kill them instantly without any twitching in most cases. When I put down larger numbers I use dry ice I purchase from my local supermarket, placing it in a cannister with hot water then plaacing the cannister in with a group of rats. It's fairly quick and painless for the rats. The Co2 tank is a great way and I plan on getting one set up as soon as the production in my colony is up to where I want it to be.

good luck.

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