Continuity mistake: During the opening credits, while the main character is clowning around with the sign the same passersby (in particular two women - one with a blue coat, the other with a plain light brown one) keep walking past him in multiple shots. (00:01:35)
Continuity mistake: Just before Arthur is hit with the yellow sign there is a person behind him that disappears between shots. (00:02:45)
Continuity mistake: When Arthur Fleck gets hit by the yellow sign, the sign breaks in two different ways in the two separate shots - the first time it is evident that the bottom half of the sign splits further in the middle, while in the wider angle it stays largely intact. (00:02:50)
Continuity mistake: When he gets hit by the sign, the round spinner on the back of the sign disappears. (00:02:50)
Continuity mistake: When Joker is beaten up at the beginning of the movie, he changes position on the ground between shots. The pieces of the sign next to him also change position; in the last shot that lingers till the movie title pops up, the part with the letters "ST GO!" is face up, it was not in the previous one. (00:03:05)
Continuity mistake: Talking with his social worker Debra Kane, Arthur is moving his legs nervously as she asks him about the journal. In that shot his cigarette is almost smoked to the filter, but in the next one there's still an inch to go. (00:05:35)
Continuity mistake: During the scene when Arthur is making funny faces at the kid, the hair wisps on Joaquin Phoenix's forehead change position between shots. The mother also turns slightly towards him in almost every cut, but his antics are in continuity. She keeps 'just noticing' him and turning towards him without the opposite movement to balance. (00:07:45)
Continuity mistake: When Arthur imagines that he is on Franklin's TV show the button on Murray's jacket is off then on. (00:12:20)
Continuity mistake: The first time we see Randall, he hangs his clown suit next to his locker; his right hand drops, but in the next shot it starts still up. (00:15:50)
Continuity mistake: In the close-up of the gun at the beginning of the scene when Arthur is watching "Slap that bass" from "Shall we dance", notice in background the bullets; there is one angled parallel to the gun and 3 more at a slightly different inclination, plus one at right angle with the first (plus other 2 not quite aligned with the rest). A couple seconds later he aims the gun at Fred Astaire, and that group of bullets changed angle entirely. (00:22:10)
Continuity mistake: Arthur inadvertently fires a gunshot in his living room. Right as he tumbles across the table, he knocks off the table the paper bag the gun came with, and knocks towards the edge of the table a pill bottle. In the closer angle shot when he cranks up the volume of the TV set, the bag is still on the table and the bottle is gone. The newspapers are also positioned differently. In the next shot we're back to the previous state (pills up, bag down, newspapers closer together). (00:23:10)
Continuity mistake: Arthur is taking notes during the standup comedian's performance. There are a cigarette lighter and a packet next to him on the table; in the close-up that follows, they have changed position. (00:25:45)
Continuity mistake: Right at the beginning of the dance in the children ward, the kid with a blue hat on Arthur's right is sitting cross-legged with the hospital robe covering his calves and feet. At the first cut, his jammies and socks become visible. (00:28:05)
Continuity mistake: In the last couple of cuts preceding Arthur's gun accident in front of the kids, the nurse's hands are not where they should be at the cut; her hands are on the kid' shoulders, then ears, before the cut she raises them to dance on the spot, but they are back on his shoulders in the next shot. The baby patient himself when Arthur drops the gun suddenly has his hands up under the chin. (00:28:25)
Continuity mistake: In the first shot of the pediatric ward you can see on the left aisle a plush ladybug toy. When Arthur drops the gun, the toy suddenly between cuts is found in the arms of a patient, and then on the bed by him. (00:28:30)
Continuity mistake: In a close-up, Arthur grabs with both hands the gun he dropped and kicked across the hospital floor, but in the wider shot that follows he's using only the left hand, and it's also clear that Joaquin Phoenix's body is turned in a complete different way, with his feet adjoined instead of the open legs seen before. (00:28:35)
Continuity mistake: One of the Wall Street Three begins approaching Arthur, and doing so he grabs the vertical support and spins around it. There's a cut mid-spin and his buddy in the background is standing in different positions; first he is laughing leaning against the support closer to him, then he is in the middle of the subway car holding two poles. (00:31:20)
Continuity mistake: Arthur tries to get up from his seat, but one of the yuppie bullies restrains him. Then the lights flicker for a moment, but it's an editing trick, as something else changed in the car; the chips' paper bag that was sitting on one of the seats in the row facing Arthur's, is suddenly gone. It comes back right after, when Arthur is struck down by the punch, and it keeps coming and going. For instance; Joker shoots the second guy dead? Bag's on the seat. Third guy runs away? Bag gone. (00:32:05)
Continuity mistake: When one of the Wall Street Three charges the punch to hit the not-yet-Joker, his buddy in the background holds Arthur's bag with the hand on top, to the point that right before the cut his thumb sinks in the bag making it bend. When the punch lands, he's holding the bag by the side. (00:32:15)
Continuity mistake: The last of the Wall Street Three is shot as he tries to flee; he falls down in two very different takes. In the side view he choreographically falls with the jacket rolling up his back, and with the left leg (initially) forward, foot on the ground. In the previous view, camera behind Joaquin Phoenix, he fell with the sole of that foot kicked back, and with the jacket still down his back. (00:32:25)
Answer: In the movie Arthur is an adult. He would have been separated from her as a child but, once he turned 18, if he wanted to live with his mother as soon as she was released nobody could stop that.
lionhead