I had an old pre-kill board. I'm doing f/t now, but if I bred rats for feeders I'd make myself another because it killed so quickly and cleanly.

It had pairs of 20 penny nails driven into it with gaps between the individual nails in the pair at increasing intervals--from about 1/4" up to the width of a large rat's neck, each pair spaced about a foot from it's neighbor. I placed the rodent's neck between the tightest pair of nails where it would go with a close fit. (hint--cut the heads off the nails and file them smooth after you've pounded them in--makes for easier and quicker setting) When the rat's head was immobilized in the improvised stock, I took the tail and pulled it so that the body was at a right angle to the direction the head was pointing and gave it enough of a tug that I would feel a "give." (another hint--you don't have to give it your all, just a smooth firm pull because only monitors and tegus like decapitated rats) That broke the rat's neck quickly and conveniently then all that was left to do was to lift the rat off of the board and present it to the intended diner.

Takes only a few seconds to kill a rat once you've done it a few times. I used a piece of scrap 2x6 for the board. Hold the rat's tail in your dominant hand and pin the board to a secure surface with the other hand. Once you get the hang of it you can dispatch rats quickly and efficiently and to my mind it's a lot more humane that the multiple "thunks" it sometimes takes with the swing-the-rat-by-the-tail technique.