Smoking
Back in the late 19th and early 20th century, when the damaging effects of nicotine weren't yet discovered or widely accepted, smoking was used not only for recreational purposes, but also as a medical treatment. It was used for various ailments—including one of the most ridiculous—asthma.
#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?)