Using exhaled breath to create co2?

[mr_weatherby]

I want to start breeding my own mice just to try it, but that is not why I'm posting.

I'm posting because someone told me of a way, to euthanize a mouse. Everyone pretty much knows the old gas chamber trick with a co2 tank or vinegar/ baking soda, etc. The way that she mentioned, was to hook a straw to a piece of tupperware, poke a small hole in the lid, and breathe slowly into the straw for 45 seconds (pinching the straw to re-inhale). The idea is, that the co2 created by exhaling will put the mouse down. She claims to do this with her mice, but I have my doubts.

Anyone else ever heard of this and/or know how effective it is?

I know that may be a stupid question to some, but I'm asking for the sake of future knowledge.