Why not just feed live? if you have the rodent live just feed live .. end of problems...If u have to kill for some reason i agree that for one mouse/rat cervical dislocation is the best. If you don't like doing that and don't mind driving to the store u can get a chunk of dry ice for like 50 cents so its not exactly a bank breaker for whoever said it cost money lol, and if it gives u peace of mind killing them that way then go for it