Perhaps you've become inured to the "human blockhead" routine, simply because it's pretty popular in sideshow culture and has been for a long time — but it can be argued the blockhead deserves a place on the list exactly for that reason. An act where one determines the exact location a sharp object can enter the nasal cavity, and then physically jams said sharp object into the location with force and precision is totally bizarre.
The blockhead routine works by taking advantage of our basic anatomy. The nasal cavity has space in which a nail, a drill, a spike or some other horrifying object can glide in without damage or pain. (Well, with plenty of practice. Try it at home and you'll encounter plenty of damage and pain.)
But perhaps the most bizarre part of the human blockhead routine is that one of the biggest risks is sneezing. Sneeze while inserting a nail into your skull, and you're at risk of serious injury. And unfortunately, you're also tempting a sneeze by tickling that nasal cavity. So in what is one of the weirdest sideshows ever, you get one of the most bizarre dangers: Controlling that sneeze reflex could be life or death.