I take the mouse or rat in the tail and bang its head into something hard. This is very effective and fast! After this I pull head and spine apart to be 100% it is dead. I really don't think anyone can come up with a faster and more humane way - well maybe dynamite
It's only effective if you manage to kill the mouse/rat in one swing.
1.0 Western Slender Glass Lizard; Logos
0.1 Charcoal Cornsnake; Morana
1.0 Golden Gecko; Smoothie
1.1 African Plated Lizard; Cypher and Nara