Hellrazors, snuffers... any 3-blade head where the blade runs all the way to the point can easily be sharpened by laying the head on a flat file and pushing it across. Make sure to push it point to back, like how the head would enter an animal. Sharpens two blades at once. Run it 3 or 4 times across the file (not applying a huge amount of pressure), flip it to the next two sides, do likewise, then flip it again for the final two blades. You might have to run the circuit a time or two, depending on how dull the blades are to begin with. You can feel the resistance and the file cutting the metal... it doesn't take too much pressure if your file is good and sharp.

Final step: Run it the same way across a butcher's steel a few times. It should shave the hair right off your arm at this point. If not, go back to the file and repeat.