Continuity mistake: When Emma lands and Hook land in the apartment after going through the portal, Henry and Regina help them both to their feet. In the first shot, Regina is seen holding onto Hook's arm as he and Emma get up. In the next shot, she is holding onto Emma's arm. (00:34:45)
Continuity mistake: Regina is talking to a young Snow White about how her love ran away. Her lipstick goes from a bright pink to a brownish red when the shot changes angles, and stays that way the rest of the scene.
Continuity mistake: When Henry is sitting at the bar at the end of the episode, reading his storybook, in some shots, there is a picture on one page, which takes up the entire page. In other shots, there is a different picture there, which takes up only half the page and has text next to it. (00:37:25)
Continuity mistake: When Emma and Hook are walking down the street in the beginning of the episode, the time on the Storybrooke clock tower is 8:45 PM. When Mr. Gold is inside the clock tower in the next scene, the time on the clock (seen from inside The Tower) is 8:30 PM. (According to the Blu-ray commentary, the scene with Mr. Gold in the clock tower was originally supposed to take place before the scene with Emma and Hook. This was changed during editing). (00:02:40)
Revealing mistake: When the newly hatched dwarves are being cleaned, there is a shot where Sleepy is seen from behind as he's drying himself with a towel after getting out of the bath tub, and you can see that the actor is wearing black shorts underneath. (00:09:45)
Continuity mistake: When Gideon shows his father the book that Belle gave him, "Her Handsome Hero", in the close-up, the cover of the book is facing upward. In the next shot, where Mr. Gold takes the book, the cover is facing downward.
There's No Place Like Home - S3-E22
Continuity mistake: When Prince Charming shows Snow White the wanted poster, the poster does not have Snow White's name on it. Two shots later, he's still holding it up, but now the poster has her name printed on it. (00:05:30)
Continuity mistake: When King Fergus signs the witch's contract by stamping the hot wax with his ring, the seal is placed right on top of one of the last word of the final paragraph. When the witch shows Merida the contract two years later, the seal has moved several centimeters below the contract. There are also subtle differences in the witch's handwriting. (00:04:45 - 00:06:45)
Continuity mistake: When Zelena is impersonating Mother Superior, she wears a nun outfit with long sleeves. When the real mother Superior enters the room, the latter is wearing an identical outfit, but with the sleeves rolled up. However, in the shot after the real Mother Superior asks "Who are you?" it switches, with Zelena having rolled-up sleeves, and Mother Superior having long sleeves. (00:05:15)
Revealing mistake: When Hook and Mr. Gold are dueling aboard The Jolly Roger, in several shots, you can see that the ones fighting are not Colin O'Donogue and Robert Carlyle, but their stunt doubles. (00:28:25)
Continuity mistake: When Jefferson hands Emma the scissors, the sharp end is pointing towards Emma. However in the next shot the sharp end is pointing in the opposite direction. (00:24:35)
Revealing mistake: After Mr. Gold's group leaves Mary Margaret's apartment, in the wide-shot where Mr. Gold asks Cruella and Maleficent to follow Regina, a direction sign pointing to a shop called "Steveston General Store" can be seen on a building. Steveston is the Canadian town which doubles as the town of Storybrooke on Once Upon a Time. (00:14:30)
Continuity mistake: As Dr. Jekyll leads David, Hook, Mary Margaret and Zelena through the marketplace while they try to escape from Mr. Hyde, as Hook says, "Next time, try an aggressive bunny rabbit", he is wearing a ring on his index finger. Two shots later, as they group heads into the alley, the ring is gone (only three seconds have passed, and since Hook only has one hand, he could not have taken it off that quickly). In the next shot, the ring is still missing, and the camera stays on Hook the whole time, but in the next shot, the ring has mysteriously reappeared.
Revealing mistake: When Mary Margaret and Regina engage in a sword fight in the sheriff's office, in several wide shots, the faces of Ginnifer Goodwin and Lana Parrilla's stunt doubles are visible. For example, in the wide shot where Regina is bending Mary Margaret across the desk and David says, "Careful", Lana Parrilla's stunt double is seen. (00:30:20)
Revealing mistake: When Hook attacks Mr. Gold, if you watch as he pushes Emma out of the way, you can easily see that one who actually pushes Jennifer Morrison is Colin O'Donoghue's stunt double. When Hook pushes Mr. Gold against the security gate, it is the stunt double who pushes Robert Carlyle. (00:18:25)
Continuity mistake: When Emma and the others return to Storybrooke, in several shots, like when Regina exits Emma's car, the Storybrooke Cannery appears in the background, painted in white. However, when the magic is released from the Olympian crystal, there is a shot where we see a wave of magic move through Storybrooke Main Street, where the top half of one of the cannery buildings is painted in red.
Continuity mistake: The headstones and statues around Regina's heart vault change dramatically throughout the series. For example, when Emma and Graham find the vault in "The Heart is a Lonely Hunter", there are two headstones on the left hand side of the vault, which are parallel to the side of the vault, and a statue of a woman on the right hand side. When Mary Margaret and David are standing outside the vault in "The Queen Is Dead", there are two completely different headstones on the left hand side, which are perpendicular to the side of the vault. There is also a cross-shaped headstone there, which wasn't there before, and an angel statue, which appeared on the left hand side of the vault when Regina went there in "The Doctor", is gone. When Regina is inside the vault with Mr. Gold in "Welcome to Storybrooke", in the establishing shot, two headstones with a cross engraved on them can be seen near the vault, but these headstones were not there in previous episodes. When Regina goes to the heart vault with a disguised Peter Pan in "The New Neverland", the statues are gone, and there are hardly any headstones around the vault at all. When Emma leaves the vault in "Breaking Glass", the statue on the right reappears, but there are no headstones in front of the vault; however, when Regina is locked inside the vault in "Shattered Sight", there are several headstones in front of it, and the angel statue on the left is back.
Continuity mistake: The location of Regina's heart vault changes throughout the series. For example, when Emma and Graham find the vault in "The Heart of the Lonely Hunter", when Regina and a disguised Peter Pan go to the vault in "The New Neverland", and when Regina hides Zelena's pendant in "Kansas", there is a slope on the left hand side of the building, but when Mary Margaret and David are standing at Johanna's grave in "The Queen Is Dead", when the green smoke goes out of the vault in "Kansas", when Regina is inside the vault with Henry in "The Apprentice", and when Regina is trapped inside the vault in "Shattered Sight", the terrain on the left hand side is flat. The trees around the vault also differ between these scenes.
Going Home - S3-E11
Continuity mistake: When Peter Pan removes the enchanted black leather cuff from his arm, he uses his magic to transfer it to Mr. Gold's wrist. However, as he sends Mr. Gold flying across the room, there is a close-up of Pan's arm, where the cuff is back on his arm, next to the normal brown cuff that he usually wears. (00:21:20)
Continuity mistake: When Will is trying to break into the library, the sign on the door, with the opening hours, is blue. When Will and Robin enter the library, as the door closes, the sign is black. (00:35:15)
Answer: He knows who she is because he knows that the fairy tales are true. He was also shown to sneak out to go see Emma or someone else. Sometimes he succeeded, sometimes he didn't. This is how he knew to look for her despite his strict mother.