I also read somewhere that you can use dry ice to create the co2 needed to 'put them to sleep'. We have a grocery store down here that sells dry ice. I think you put it in a bowl and add water....place that in an air tight container (like a cooler) and place the rodent in as well. Close it for a few minutes and that should do the trick.....I've never done this however. Actually, we may have to try it for Smitty b/c he simply refuses f/t.