Originally Posted by
mdarnton
The "slice" thing: when you chop up bread from the loaf, you don't just try to push the knife straight down, you slice, and it works better. Same for shaving. You can either push with the razor at 90 degrees to the line of movement and slide the razor sideways as you do, or turn the edge at an angle to the direction of the cut, as on a guillotine. Or both.
The slicing is like sawing. Guillotine is a bit more esoteric: what it is actually doing is effectively reducing the 15 degree cutting angle of the blade to something even smaller. At a 45 degree angle you're down to a 7.5 degree effective cutting angle. Nifty.
You want to have pretty good control before you do this: no one here wants you to slit your throat while shaving.