Factual error: Towards the end of the movie, two characters finally make it to a Louisiana sheriff's office. The sign out front reads, "Vierge County." There are no counties in Louisiana, only parishes.
Factual error: It is not possible to have a conjoined twin of the opposite sex. They are similar to identical twins, which are always of the same sex, in that they are formed from a single zygote. In the case of conjoined twins, the zygote fails to divide normally.
Suggested correction: There are always exceptions to the rules and, although VERY rare, it IS possible for conjoined twins to be - rather, end up being - different sexes. There are about 10 documented cases. In one case, is my understanding the conjoined twins started out as males but a genetic mutation (or something) occurred and one male lost his Y chromosome, thereby developing into a female with no ovaries. (The now-female twin would have so-called Turner Syndrome.) I don't have any sources to quote off-hand.
The male would have lost his Y chromosome after the zygote "split", but he was a monozygotic male.
Other mistake: Despite being a deadly marksman (only a few minutes earlier in the movie he stopped a bullet directed at him shooting it off the air), Bloodsport snipes several times at the huge kaiju featuring a massive eye in the central part of its body, and never once hits it. (01:51:45)
Factual error: When Ed and Lorraine Warren are trying to convince the lawyer to represent Arne, there are is a copy of "Jonathan Strange and Mr. Norrel" on the shelf behind them, which was published in 2004. The film is set in 1981.
Continuity mistake: Maddox has blue eyes as a teenager and dark brown eyes as an adult.
Factual error: James called the "Washington Board of Psychiatry" to file a complaint against Dr. Clark (Philip). Complaints (which need to be WRITTEN) against medical doctors are filed under a State's Medical Board, which would be the Washington Medical Commission in this case. Washington has a Board of Psychology and there is a Washington Psychiatric Society, but there's no "Washington Board of Psychiatry" per se (and even if there were, a complaint would still be filed with the Medical Commission).
Continuity mistake: Danny's car is shown going over the cliff twice - before and after Danny shoots himself. Right before going over the first time, Danny is shown with his right hand on the steering wheel but the second time with his right hand on the rifle (which is pointed toward his neck). (00:32:22)
Continuity mistake: Although the amount of alcohol remaining in the bottle had been slightly reduced, the reduction was too negligible to have filled the Game Master's glass to the level shown after his telephone call to Sienna. (00:06:57 - 00:08:46)
Continuity mistake: After Diane lit and switched her cigarette to her right hand (and off-camera), most front views of her left arm showed it in front of her, along her stomach, but rear views showed her holding the cigarette in her left hand with her arm more perpendicular to her stomach. Whether her left elbow was fully on the table or over the edge also varied numerous times. (00:08:00)
Continuity mistake: Helen's slipper is at about a 45° angle toward the right of the screen when Miss Willoughby finds it. When Detective Jimmy shines his flashlight on the slipper, it is facing the opposite direction. The second time Jimmy shines the flashlight, the slipper is at a steeper angle. (01:00:33)
Continuity mistake: The dead rabbit was thrown onto its left side with its back almost parallel to the table's edge (width) and its nose/head almost in the corner. There was a bowl of several brown eggs several inches away from the rabbit's stomach. When the camera shifts, the rabbit's head has shifted at an angle away from the corner, its rear feet are slightly hanging over the table's edge (length), the bowl of eggs is touching the rabbit's stomach, and the eggs are piled on the opposite side of the bowl. (00:05:35)
Revealing mistake: The blemish/mole that was on the right side of Ghost's nose showed up on her left side (and she was not looking into a mirror). (00:57:40)
Revealing mistake: The possessed "Helen" that Fr Daniel threw to the ground by grabbing the back of her hair landed like a stuffed doll, not person. The "body" was mostly padding and the fake "Helen" kind of bounced or teetered after hitting the ground. Also, her arms stayed hidden in front of her whereas a real person would be stretching out or moving arms to try to land as safely as possible. (00:21:35)
Other mistake: The chances that no-one in the approaching truck - three men, including a man standing in the bed facing oncoming traffic - would notice that Danny had a front seat passenger are very low, if not zero. Even after Motley got into the second row seat of the truck, but did not get down right away, the men in the truck had turned around and were following Danny but still did not notice Motley. (00:10:00 - 00:10:27)
Revealing mistake: At first glance, the cow at the start may have looked real, but its limited mouth movement while eating grass (without any grass being pulled out) indicates it was a mechanical cow. The cow also did not move its rear end or raise its head when Fenn and Geary approached and stood right behind it. A real cow would not stay in the exact same position (motionless) that amount of time. The cow's "fur" also did not look real. (00:02:50 - 00:03:24)
Continuity mistake: The bull horns and skull attached to the front of Doug's SUV were much larger on his way to the site than when he pulled up to the meeting spot. Initially, the horns spanned past the low beams, but were some distance from the low beams on each side when he arrived. The overall size of the skull was noticeably smaller and looked less menacing. (00:20:03 - 00:20:35)
Deliberate mistake: The angle of the light coming from the film projector (which was up high on the back wall) was too high to actually project onto the screen across the room. Also, people were standing in front of the screen and should have been blocking part of the projection and have light on their backs but did not. The screen operated more like a DVD player on a TV. (00:35:20)
Character mistake: Over the phone, Julie told her sister Sara, " I got them [parents] a bouquet", pronouncing the "T" in bouquet. Bouquet has French origin so the "T" is silent. Bouquet is properly pronounced like bow-kay (American English) or boo-kay (British English). (00:00:55)