just a side note, but for mammals, to die from CO2 is terrible. Its the worst choice of all gas you can easily get. The problem is that mammals, as well as humans, react with panic and painful reflexes and cramps and convulsions if CO2 goes up.


Use nitrogen or helium or argon, these take a long time to work but a mammal will notice absolutely nothing, because mammals can only detect CO2 buildup, not lack of oxygen. Best choice would be nitrous oxide, its also painless and knocks out mammals faster than anything else.

or just freeze it. Still better than CO2 i think, since humans that almost froze to death report that it doesnt feel bad, while humans that almost got strangled or drowned or almost died because of lung problems report terrible agony and pain and panic, due to CO2 buildup.

Really, people want to kill rhodents humanely, and then end up torturing them to death because they pick the wrong gas. Tragic irony.