(at around 8 mins) When Joey bursts into the ER room, she witnesses a patient's head explode. As she staggers out however the patient can be seen lying on the gurney with his head very much intact.
(at around 36 mins) When Joey is playing through the video from the asylum, the video suddenly cuts to a man who tells her that the woman subject in the video is telling the truth. She rewinds the tape, but the screen is now blank. However, the reflection of her glasses clearly show that there is still a man on the screen.
(at around 1h 14 mins) When Pinhead is in the church, he stands behind the table, and the candle to the right of him is straight. He then pushes the cross off the front, look at the candle, it is now on a slant then in a split second the candle is straight again as if it had never been touched.
(at around 1h 6 mins) Joey finds Doc has been decapitated in the club yet his head is intact when he comes after Joey as the Camerahead Cenobite. When Joey sees him without his head, he was in the process of being made into a cenobite.
(at around 59 mins) When Pinhead is just about to start killing everyone in The Boiler Room night club, a man catches the first hooked chain that Pinhead unleashes. Yet when you look closely as you see the man holding the chain there is no hook, but a piece of wire.
(at around 1h 9 mins) When Joey is running down the street away from the club, 2 pedestrians can be seen walking on the opposite side as if nothing unusual is going on.
In the scene where Joey is at her desk, after the dream of her father in Vietnam, talking to Terri there is a shadow box of Joey's dad's awards and rank. There is Sergeant (E-5) rank in the box, the chevrons tops are pointed down, the US Army's chevron points up.
When Joey Calls Doc the news on the T.V. states that camera crews were at the Boiler Room along with police and that several bodies are being removed but,When Joey arrives there are no police or camera crews to be found. (Correction: that news report Joey sees is a ruse from Pinhead to get her to the Boiler Room, evident by Doc not finding the report and also the camera revealing that her TV isn't even plugged in.)
(at around 1h 11 mins) When the Barbie Cenobite breaks through the brick wall, the bricks wobble when he touches them.
(at around 1h 8 mins) When the cab swerves to avoid hitting Joey, it hits a light pole. But the pole sparks before the cab ever hits it.
(at around 19 mins) The rat bite J.P. received is deep enough to bleed quite a bit onto the statue yet there's no sign of injury on either hand in later scenes.
(at around 9 mins) When Joey is sitting down inside the bus, she is resting her head on a window. We hear a bang on this window, and Joey she is startled. The camera shows us a haggard man banging and groaning for about 2 seconds in frame, yet this is impossible as the bus Is moving the entire time. The man would have to be an extremely fast runner to do what he is doing, all the while remaining in constant speed with the bus.
When Joey first meets the ghost of Captain Spencer, he is sitting a hut. The walls indicate that it's a Quonset hut, a US military design dating from 1941. But all the indications are that Capt. Spencer was a WW1 British officer. He should be sitting a Nissen hut, a military design dating from 1916.
Pinhead cannot touch the puzzle box but has no problems doing this in the previous films. Pinhead can't touch the Lamont Configuration in this film because he is separated from his soul/Elliot Spencer.
(at around 1h 8 mins) None of the Boiler Room patrons make it out of the club alive and Joey has to step through all the bodies before she meets Pinhead but she has no problem getting past all the corpses and onto the street without him stopping her.
(at around 44 mins) When J.P. is asking Terri to get close to him, the shadow of the boom mic can be seen on the statue.
(at around 56 mins) While Elliot Spencer is talking to Joey in her dream, Doug Bradley mispronounces the word unstoppable as "unstoppabubble."
56:33 minutes in the movie, while Elliot Spencer is talking to Joey in her dream, Doug Bradley mispronounces the word unstoppable as "unstoppabubble."