Wikipedia is not a reliable source for info. It's humane because they don't know it happened.

Let me try again since you seem to not get it.

WHEN DONE PROPERLY THEY GO TO SLEEP FIRST, AND THEN THEY NEVER KNOW WHAT HITS THEM!

There is no pain, there is no snapping of a neck, it's just sleep and then bye bye. You know how they do lethal injection? They put you to sleep and then kill you. Same thing with the mice/rats.

It is, WHEN DONE PROPERLY, the absolute most humane way to kill them.