Sentence:  He is a classic sideshow performer, entertaining crowds with feats such as sword swallowing, fire-eating, and chainsaw juggling. His specialty, however, is the human <WSD>blockhead</WSD> act, hammering six-inch nails up his nostrils. 
Meaning of the word marked with <WSD> tags:  A sideshow performer who hammers nails or similar items through his or her nostril into the nasal cavity; human blockhead.