Revealing mistake: When Pinhead is killing the patrons at the club and they are running away to try and escape, you can see some of them laughing instead of screaming like they should be.
Revealing mistake: After Joey runs from the club into the street and a car swerves to avoid her, it hits a lamppost which causes sparks; but look closely and you can see that the sparks appear just a split second before the car actually hits the post. The sparks were rigged and set off a second too early.
Revealing mistake: When Joey stumbles into the church, there are a few wide shots where you can tell the background is mostly a matte painting. What gives it away is that the candles in the foreground are flickering while the candles in the background aren't since they're painted.
Revealing mistake: When JP gets the two pistons shoved through his head and we see them "break through" his head, you can tell it's just two different takes of the same effect, since both come out ABOVE his ear, whereas when we see the final result, there's one coming out BELOW his ear. (The hairline on the fake prop head is also a little wonky.)
Revealing mistake: When Pinhead is in the statue talking to JP, you can see where the makeup ends around his mouth/lips during his close-ups, especially when he spits out the bullets.
Revealing mistake: When the CD's embedded into the DJ's head, the second CD we see cut into his skin has fishing line coming off it.
Revealing mistake: During the nightclub massacre, there's a brief shot of a woman having the skin around her eye pulled off. You can tell that she just had some fake skin over her face and had her face painted with a "blood" texture beneath. The effect is incredibly cheap and unconvincing.
Revealing mistake: When the former bartender-turned-Cenobite blows a hole through the brick wall and comes out, you can see the "brick wall" bend like foam or rubber as he comes through, revealing it's a fake prop wall.
Revealing mistake: When Joey is running around the streets with the box, the former bartender Cenobite blows a hole through the wall and comes out. There's a brief shot of Joey cowering with her back to him, and you can plainly see one of the supposed "bricks" from the wall literally smack her on the side of the head and harmlessly bounce off, revealing it's a lightweight foam replica. The scene tries to cover by adding in her grunting "Ugh!", but if it was a real brick, it would have knocked her right out.
Revealing mistake: When Pinhead pulls the pins (with attached worms) out of his head, there are two brief flubs. In the first close-up, you can see several of the pins on his head "wobble" unnaturally, revealing that it's likely some sort of rubber prop head. When he pulls the second pin out, the camera is in almost the exact same position, and he appears to pull the second pin out of the exact same spot, so it's likely just two different takes of the exact same effect.
Revealing mistake: When Pinhead is walking into the church, the stained-glass windows start to explode. In several of the close-up shots, you can see the supposedly stone walls of the church "wobble" as the windows explode, revealing they're just painted set walls.
Revealing mistake: When Joey sees the man's head explode in the hospital at the beginning of the film, pay attention. You can tell that the head was sculpted out of rigid foam (likely something similar to Styrofoam), painted, filled with fake blood, and then blown up. What gives it away is that you can see some of the unpainted white foam on some of the "chunks" of his head.
Revealing mistake: When Joey gets "cut" by the chain in the hospital in the beginning, pay attention. In the shot where she gets "cut," you can plainly see all that happens is the chains slap a little blood on her ankle without any signs of actual damage. Then, a few shots later, there's a very quick closeup of the "cut," and you can see that all they did was paint a little gooey "blood" over the top of her pantyhose, which aren't ripped through at all. (Nor is there a visible cut, either).
Revealing mistake: When Pinhead kills Sandy, his chains attack her, then they lift her up, and her stunt double is visible because her hair is much shorter and her face is completely different.
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