humanly euth mice?

[distaff]

I use a blow to the head with a hammer. Easy, and instantaneous.
My snakes don't mind the bloody heads.
I can't see how CO2 is more humane than that, but to each his own.

Same method for the chickens and rabbits we butcher for our own meals.
A bigger animal just calls for a bigger hammer. It is over fast.
A little prayer helps.

Letting nature take it's course, in the case of tumors seems like possibly a hard way to go.