Factual error: While handling the ignition coil cable to the distributor cap, Joe Pesci tells De Niro that the timing chain needs adjustment in his truck. A truck of that year with an inline Chevy motor would not have a timing chain at all, instead this truck would be equipped with a direct drive timing gear. Even if it had a timing chain, it would be behind the water pump and a cover. It would have been a several hour job to replace, not possible to adjust it.
Visible crew/equipment: When Lionel returns to the jazz bar and discovers Billy Rose has been killed (framed as a suicide), you can see two people standing in the shadows to the left of Lionel as he enters the main room where the stage is located. A man is hunched over, whilst a woman is standing still wearing what looks like a dust mask. (01:32:27)
Factual error: Based on the films being shown at the theater, the movie appears to be set in 1981. One of the TV commercials shows the Energizer Bunny, which didn't make its first appearance until 1988.
Continuity mistake: In Maney Gault's first scene, the porch he is lying on loses a screen covering for the closeup, only to regain it for the third shot.
Continuity mistake: There's a clear mix-up in editing during the car chase. Marta checks her phone twice for Blanc's calls as she tries to get away from the police. The first time the phone signals 9:36 AM, the second time 9:34 AM. (01:31:50)
Other mistake: During the restaurant shoot out between Jr and the bad guys, he takes Sasha's weapon (Kel-Tec P-3AT) and opens fire on the bad guys. The Kel-Tec P-3AT is chambered in .380 and holds 6+1 rounds. During the firefight, Jr fires 9 times. We also see the bottom of a spent casing and it shows .22. (01:12:00 - 01:13:00)
Continuity mistake: After Sandler shaves in the cabin he gets back on the deck unshaved. When they appear at the dinner he is shaved.
Plot hole: Dr. Seager told Beth that "It [Z] was all in her head" and only she could stop it. How, then, did her son Josh have the same "imaginary friend Z"? Moreover, if Beth had Z as a friend when she was eight years old, why didn't she remember him or have her memory jogged when Josh first told her about his friend Z? Also, if Beth told Z that they would be together forever (get married and have a lot of kids), why would Z need to go through Josh to get to her?
Continuity mistake: En route from the front door of Wayne's mansion to the table in the Batcave, the pile of pizza boxes in Alfred and then in Mike's hands continues to change in size and number: at first the pizza girl delivers 11 boxes, Mike slams on the table just 8, but he brought down the stairs twice that amount (without counting through freeze-frame the precise numbers, it's simply obvious at first glance that the pile is bigger in some shots and the pizzas themselves are pictured of inconsistent size).
Character mistake: Toward the end of the film, Detective Davis orders Captain McKenna to put his badge on the table. New York City police always refer to their "shields", not badges.
Continuity mistake: At the ATM, when Ramona is pulling money out, you can see the reflection of a police car pull up behind her. It pulls up just as she begins to turn around and nobody is getting out in the reflection nor are lights on. But suddenly when she turns around several officers are already standing with guns trained on her and the lights on.
Continuity mistake: Right after the scene where Nels saws up his gun, he walks into a store with his arms folded. His hands are down close to his stomach. When it cuts to the next angle, they are much higher at his chest. (00:26:51)
Factual error: As well as the sergeant's stripes on his cuff, Sergeant O'Neil wears three pips on his epaulettes, which would indicate a much more senior rank and would not be worn together with the stripes.
Character mistake: Detective Spitzer went into Harper's dark/unlit house, saw his partner Greg on the floor, and then saw Alec standing in the kitchen. Without identifying himself, telling Alec to drop his weapon (pistol pointed toward the floor), or bothering to determine what happened, Detective Spitzky shoots Alec. (01:27:08)
Character mistake: Right at the beginning of the movie, introductory technobabble. "In this canister, there's a solution of protons. The canister is attached to a rotor circuit that generates the protons to the speed of light." I believe the science genius and creator of time travel mixed up the words "generate" and "accelerate" here. (00:00:50)
Other mistake: Jesse does not talk because of his traumatic childhood (which includes being kidnapped at a young age by Mr. Charlie), so it doesn't make much sense for him to be the narrator.
Character mistake: Queen is an attorney and should know how to conduct herself as a passenger in a car pulled over by police, yet she fails to behave in an acceptable way. Even though certain things may be permissible under certain circumstances, a lawyer should know exceptions and extenuating circumstances, but she apparently does not. She did not have the right to interfere with a police officer and "demand to know" or get out her cell phone to record if she was told to keep her hands where he could see them. (00:10:25)
Factual error: In 1940 3 of Alf White's men are arrested. As they are taken out of the pub they were in Alf and his son stand in the doorway. To their left (viewer's right) are posters for Floyd Patterson (who would have been aged 4 or 5 at the time) and the Platters (formed in 1952) and Lonnie Donegan (started performing 1949). (00:20:03)
Continuity mistake: When Trip is holding up Frank in his room, he's holding his gun sideways. But in shots from the front, it's tilted at about a 45-degree angle, but in shots from behind, it's almost 90 degrees to the side. (01:10:05)
Continuity mistake: In the graveyard, Frank is talking to Charlotte next to a tree. It cuts to a shot of Swilly for a brief moment, then back to Frank and Charlotte again, and suddenly he's standing much closer to her. (00:16:36)