4. The Head Crab (The Thing)
This 'decapitation' is something a little different to the others in the list up to this point, in that it isn't inflicted by another person. When Norris has what appears to be a heart attack, Copper attempts to revive him by using a defibrillator. After saying "clear" and going for the first pump, Norris' chest bursts open revealing a set of otherworldly teeth and bites Copper's arms off, revealing that Norris was in fact assimilated by the alien life-form that was on the loose and the body on the table was in fact the alien imitating him. When MacReady uses a flame thrower on the alien, it removes the head from the body of 'Norris' (given that every piece of the alien is an individual organism with its own survival instinct) and turns it in to a spider-like creature that has become known as the head crab. MacReady swiftly sets fire to that as well, but not before everyone present has been completely weirded-out by the sick scenario they just witnessed.