Have you ever cut a corn off of your foot using a knife? No? Hell no? Well back in the day, women needed to be advised not to do so, as shown in this 1937 ad. "Corns come back BIGGER UGLIER," reads the copy. Blue-Jay corn plasters: Better than stabbing yourself! (Click tag to see full-size picture.) [Modern Mechanix]
Am I the only one who's used those callus shavers with the razor blade? They sell them in drugstores to this day, and they rust super easily and are probably not recommended by anyone with a grain of common sense.
But... they do work, if you don't slip and give yourself a terrible bloody gash. It looks kind of like shaving Parmesan cheese. Sorry if I made anyone vomit. It's one of those things I find utterly disgusting yet perversely fascinating, like squeezing blackheads.