OTOH, I have a snake (spotted python) that eats better if she can smell blood. I don't brain, just give the f/t mouse's head a squeeze to get a little blood out of the nose. Less gory and simpler than braining (which I have done), and sometimes does the trick. Worth a try before braining, IMO.
That's a good point try a bleeding rodent first - until you mentioned it I hadn't realised mine responds with much more enthusiasm to a rodent with blood around the head.