Until reading this, I had forgotten about when I caught 16 rats in two weeks. Used a Zapper trap - a little tunnel they go in and stand on an electric plate and get electrocuted and die. You pick up trap and slide dead rat into bag and set it back in place with reset button. Red light flashes when another rat traps. I was getting three a night. Had it up with bait for a week and nothing. Got discouraged, threw bait out because it attracted ants, but put the trap back on in place. A rat went right in it without bait - I guess it made a good hiding place. they were suspicious of the bait. Hawaii has huge, smart, numerous roof rats.
Anyway, one rat was so huge only half of him fit in the tunnel - and he wasn't quite dead, breathing but out of it but coming around. Anyway, I placed a 1" x 12" section of board over him (rib cage centered) and stood on the board - and he died.
The trappers I know do the standing thing with mink, marten, ermine, and others.