Trepanation
Trepanation, the practice of drilling, cutting or scraping holes in a person's skull, has been around since prehistoric times. It is believed to be one of the oldest surgical procedures—however, scientists are unsure why our ancestors performed it. In western medicine, up until the 19th century, trepanation was widely used to treat head traumas.
#18 The idea is that of sympathetic (imitative) magic : mices have good teeth, so they are good for ailing teeth... the same kind of "reasoning" is always used nowadays in... homeopathy !
#19 Some trepanated prehistoric patients have survived long enough for the bone to grow again around the opening !
#1 Maybe one was supposed to have masturbated with a handful of cornflakes. That certainly would have made it a lot less fun. (Cream on your cornflakes, anyone?)