Continuity mistake: When Terri and Joey are talking about how Terri doesn't dream, throughout the scene she's carrying a cup of coffee. But at a certain point in the scene, her coffee cup just completely vanishes. There's no point where she sets it down. It's just there... and then it isn't. It's entirely possible she set it down in a deleted shot, but the way the scene is edited, it's all portrayed as one fluid conversation with no pauses, so it's a mistake.
Continuity mistake: When Terri is talking about how she doesn't dream, she walks around Joey's living room. The scene cuts to a different angle, and she flops down into the chair. However, before the cut, she wasn't close enough to the chair to sit down. Additionally, Joey's hands change positions between cuts.
Continuity mistake: When Terri goes to Joey's apartment and talks about how she doesn't have dreams, as she stands up, her hands go from far apart to close together between cuts.
Continuity mistake: When Joey meets JP, he offers her a rose, but when Joey walks away, it's no longer in his hand as it was in the previous two shots.
Continuity mistake: When the guy slams his hand on the bus window, startling Joey, in the first shot, only his right hand is on the window. In the next shot, he's hitting the window with both hands. He then takes his hands off the window and starts lowering them, but in the next shot, his right hand is back on the bus.
Continuity mistake: When Joey runs towards the operating room and Terri leaves the hospital, in the first shot, Terri begins to open the door and walk out in the background. The camera cuts, and we see her do the exact same thing a second time.
Continuity mistake: When Joey is introduced and says, "That's a wrap," she starts rubbing her forehead with her hand. When it cuts to an over-the-shoulder shot, she's no longer rubbing her forehead. (You'd see her hand still from the angle.)
Continuity mistake: When the cop cars explode, suddenly the cops vanish between cuts. Obviously, they were meant to be killed in the explosion, but they just aren't there in the wide shots of the actual explosion.
Continuity mistake: Joey runs up to the female cop. It then cuts to her partner getting out of his car, and you can see Joey run up to the female cop a second time in the background.
Continuity mistake: When Pinhead pushes the second nail/worm into his hand, the camera cuts to an extreme close-up. In between shots, suddenly there's more blood on his hand.
Chosen answer: It's a piston. 2 piston rods are jammed through his head and they move powered by something unknown. You can see the crank shaft and part of some sort of cylinder. A piston is part of an internal combustion engine. It's part of his cenobite form since he liked cars.
lionhead