You can “kasher” a shaver – take each blade, and rub each individual blade (the little ones) on a key several times, not missing any blades – hence blunting, and not letting the blades cut without help from the screen.
Of course, it will not shave as well, which is the point. Don’t miss any blades!!!
If you can get someone’s beard hair, see if the blade cuts the hair when the hair is held taunt. and viola.