This subject comes up from time to time. I posted a new method in a thread earlier this week. Since this method is not well known I thought maybe further explanation was in order.
There is a great deal of controversy on this subject. I have tried many methods myself. Some more successful than others. I think you need to keep in mind that the main objective is that the mouse should die quickly with as little discomfort as possible. This needs to include the discomfort of stress and fear during the time leading up to death. Many people fail to take that into consideration. I believe that as much as possible the mouse should be completely unaware of its imminent death. It’s for this reason I use a 12-gauge shotgun. I personally feel that 1 ¼ oz of #5 shot is best. This gives you a tight enough pattern to do the job and the individual pellets have enough mass to do substantial damage. For this demonstration I have chosen a Browning Citori Over and Under. The brand and model are not important to the process, use what ever you have at hand.
I think humanity demands that certain courtesies be extended to the mouse. A last meal, a cigarette, and a blindfold would be the minimum. Perhaps a few words with his family and the clergy might be in order. We must never allow ourselves to become hardened to the process. The mouse needs to be kept in mind every step of the way. This particular mouse was very health conscious and declined the cigarette.
This method is quick, efficient, and painless. As you can see, the mouse feels no distress.