OK, I think I see it... The neck/shoulder piece is pre-positioned down and in front. It is raised up and over the lady's head as she sinks down in the chair... There's nothing in the cover cloth which is there to cover the transition. There's small clues such as, no mass when he throws the "head" at the screaming lady and when the door is closing you can see a dark spot above the neck line which is either her hair or another cover cloth to disguise the flat top of the neck stub prior to pulling the stunt... Prank is not the right word... Definitely stunt and lawsuit territory! 🤣🤣🤣