Well for the last few times i've played Hitler, i just used Dry Ice. it's about 99 cents a pound and you just drop it in water and close the lid (i used a cooler) and it works the same way. problem was i bought a 10 pound block of dry ice...i only managed to execute 2 rats and a mouse....so if you can manage to find it pound by pound, or if you have 20 or so rats/mice you want to put down, it might be cheaper to get some dry ice