Stupidity: Possessed child Nicholas made the cross from a necklace pierce Fr Louis in the neck, causing blood to gush out. Fr Peter yelled, "Fr Louis, Fr Louis" as Fr Louis tried to pull out the cross. No one else present rushed over to try to help stop the bleeding or assist him. Fr Louis' sash could have been used around his neck to apply direct pressure to the wound. (Although it might have been obvious that it was a fatal wound to the neck, someone should have at least tried to help). (00:07:15)
Stupidity: When the police turn up the first time the mother lies to them to get them to go away but the burglars can't hear the conversation. She could have told them exactly what was happening and that she had to make it look like she'd got rid of them. She could have then smashed all the cameras and just let them in.
Suggested correction: This was a character decision, and a completely understandable one. Her daughter was being held hostage in the panic room. She decided to cooperate with their demands for the safety of her daughter. Your idea is a solid one, but she simply did not think of it in her state of mind. She opted to get rid of the police, and her decision is not a movie mistake.
Stupidity: The first time they see the bad guy in the Land Rover, Morgan has him in his sights but can't shoot, as he doesn't want to kill him. Clearly, the obvious thing to do is to shoot the car tires, but he doesn't and lets him drive off.
Suggested correction: Shooting out car tires is not an actual effective strategy to get a vehicle to stop. A 9mm bullet simply doesn't cause enough damage to a tire to get it to go flat immediately. It causes similar damage as running over a nail. It is a movie cliche, similar to using a gun to shoot out a lock or a rope, it just doesn't happen in real life.
Stupidity: If the weak spot of the house is the fiery chimney, then the kids could have just thrown the dynamite into it instead of lighting it themselves. They put themselves in unnecessary danger for the sake of drama.
Suggested correction: You don't think that once Nebbercracker noticed the house had the spirit of his wife, he would have realised this could happen one day. In order to protect her, he most likely blocked off the fireplace.
Stupidity: Rick tries to kill Frank at his boathouse by dumping gasoline all over the place and using Ray Coleman's lighter that Frank had. At this point, Rick has gasoline over his arm, but instead of properly cleaning it, he opens the lighter immediately and has his arm burned. Surely a criminal genius like Rick wouldn't have risked this as this is a loose end. Further mention goes to when he has the bathroom door open for no reason while medicating the burn mark, which enables his wife to see him and discover who he really is.
Stupidity: In the flashback about the way the victim was poisoned, it would seem that the murderer straight out went to a waitress and handed them a single chalice of poisoned champagne, ordering the waitress to give that exact glass to the victim. That's just a little bit absurd; if it's a flashback based on a testimony, the case should have been solved in 0.1 minutes once the waitress says that that very well known person asked them to bring a glass to the victim - it's a request highly unusual and that would be easily remembered. If it's just some wild guess of the detective, that's a mighty strange way to imagine how things went, rather than just the killer slipping venom in the victim's glass when they were not looking. (01:04:00)
Stupidity: A detective who explicitly frequents morgues not being able to tell the difference between a real slashed throat and fake blood spurted on a neck is one thing. When he returns to the room and finds the body missing, instead of becoming alert, drawing his gun, putting his head on a swivel, and warning his friend outside, he slowly walks over to examine the razor and figure out how the magic trick was performed, allowing the killer to ambush and kill him almost comically easily.
Stupidity: Considering the movie takes place in the winter of '75, it seems unlikely that the babysitter would arrive in a halter top and barefeet.
Suggested correction: I agree that this is a "stupidity", but think your use of the words "it seems unlikely" allows for the suggested corrections already given. Perhaps replace "it seems unlikely" to "it isn't rational." Even if the daytime temperature was mild for winter, the temperature would probably drop by around 30° overnight.
Suggested correction: Actually, January of 1975 was very mild, much like the winter in the northeast this year, so it would not be impossible for the babysitter to wear unseasonable clothing.
Suggested correction: Ordinarily I would agree with this observation, however, I believe the girls outfit matches her carefree attitude. She did bong hits in the family bathroom, laid on the boys bed seductively and asked him if he French kissed so dressing comfortably to babysit isn't out of context.
Adding to this, almost every babysitter I had growing up went barefoot or at least shoeless. Even this past new years eve, the young lady who came to watch my kids took her shoes off as soon as she came in the house.
It is a common courtesy to remove shoes when entering someone's home to protect the carpeting (or other flooring) from getting soiled by whatever might be on the bottom of shoes after walking outdoors.
Maybe I'm wrong, but after watching this movie last night, it sounded like the girl was wearing flip-flops when she walked across the bathroom to open the door. Would it be rational for her to have worn sandals too?
Considering she was barefoot for most of the night, yes, she may have worn them for comfort.
Stupidity: During the ghost chase montage, why would Velma look for her glasses with her hand in midair instead than on the ground? No matter how nearsighted you are, the closest wall, or obstacle, is meters away and you'll never find your glasses anywhere but the floor. She does it for a longer time than anyone would. (00:52:40)
Stupidity: The security system is able to automatically ascertain the malfunction to the exact valve, and the electrical problem, but the alarm is not triggered at that point, but only when the holding cells are already filled with water and Breslin is making his return. They are on a ship, the fact that it's taking on water feels like a pretty important issue to monitor.
Stupidity: The babies could have simply been swapped at the start. There was no reason Father Spiletto needed to inform Robert Thorn of his son's death and then convince him to take a different child instead.
Suggested correction: Perhaps, but then again the Satanists were trying to cover all bases. If they simply swapped them, the parents may start questioning things when Damien grew up and they might have noticed that he didn't look or behave like either of them. For insurance they could have brought Robert Thorn into the plot (without his knowledge of the full story), so that if she asks any questions he could simply stick to the story, offering a cover to the Satanists. During the conversation, he mentioned that the baby dying would be devastating to his wife (which is why he agreed to the switch) so his intentions were pure, even though it ends badly and tragically for both him and his wife.
Stupidity: The ending has a bit of a twist; apparently, octogenarian college professor Morgan Freeman somehow chased down and murdered offscreen 6'3" professional assassin Vernon Davis. That's not the toughest part to swallow, though; he also sent the two detectives (one of whom he is not even supposed to know of) via UPS 2-day delivery mail some body parts of his victim. We don't know which part Lavazzi gets (genitalia were mentioned earlier), but Boyd gets the eyes and decides to eat them. For starters, unrefrigerated 2-3 day old eyes would never look as pristine as the ones Boyd gets. Also, Morgan Freeman mentioned earlier in the movie that for the power of Muti to be effective, the body parts need to be taken from a victim that is alive, screaming, and eaten only mixed with herbs and other catalysts. So what the detective does doesn't make sense even in the movie lore.
Stupidity: Judy Hicks, a trained cop and sheriff with over a decade of experience, does not carry a back-up holstered gun on her when she is off-duty, one day after her son's close friend is stabbed seven times near to death. A trained police officer/sheriff would also question why the killer would tell her they are about to kill her son, before they do it, if not to bait them and lure them into a trap. (00:45:58 - 00:46:30)
Stupidity: Anyone with a job in the White House would have to be known to the Secret Service on a daily basis, so the two Secret Service agents that find Cory the janitor should have been aware of his identity without him having to state who he was and that he worked there.