Revealing mistake: In real life, the Storybrooke Cannery is known as the Gulf of Georgia Cannery, a real cannery in Steveston village, the town which doubles as the town of Storybrooke on Once Upon a Time. In most episodes where the cannery appears, the name on the building is replaced with the Once Upon a Time version. However, in this episode, when Emma is driving in her father's truck following shortly behind Cruella's car, there is a wide shot of Cruella's car turning right, and you can see the sign on the cannery, which has not been updated properly: Bizarrely, the first word of the real business name is still on the building, and the first three letters of the fictional name are missing, making the name on the building "Gulfrybrooke Cannery." (00:23:20)
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)
Revealing mistake: When Snow White and Prince Charming hurriedly make their way through the woods in the beginning of the episode, in the shot where Snow White jumps over a log, you can see the face of Ginnifer Goodwin's and Josh Dallas' stunt doubles. Josh Dallas' stunt double can also be seen as Snow and Charming are running thought the woods in the previous shot.
Revealing mistake: During the car chase scene, when Lily is driving Emma's car, there are several wide shots of the car driving down the road and you can see that the one driving is not Agnes Bruckner, but her stunt double. Lana Parilla's stunt double can also be seen in several wide shots when Emma and Regina catch up with Lily and try to overtake her. (00:30:55)
Revealing mistake: In the first shot of the scene where Emma and the others arrive in Storybrooke in their cars, on the left side of the screen, you can see a sign behind a branch. It says "Steveston Museum and Visitor Centre." Steveston is the name of Canadian town which doubles as the town of Storybrooke on Once Upon a Time. (00:07:00)
Revealing mistake: When Hook tries to rip Zelena's heart out, as a blast of magic hurls him into the wall, you can see that the one who actually hits the wall is Colin O'Donughue's stunt double.
Revealing mistake: As Hook is chasing King Arthur through the woods, there is a shot of Arthur running, where you can see that the one running is not Liam Garrigan, but his stunt double. In the next shot, Hook is hot on Arthur's heels and you can see that it is Colin O'Donughue's stunt double who is chasing him.
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)
Revealing mistake: When Hook is running from the Lost Boys, as he clambers down a hill, you can see the face of Colin O'Donoghue's stunt double. (00:00:50)
Revealing mistake: Hook's wire is visible as he climbs in Rapunzel's castle. (00:10:05)
Revealing mistake: When Detective Rogers is chasing Naveen, in several wide shots, the person running isn't Colin O'Donoghue, but his stunt double. (00:25:50)
Revealing mistake: When Emma and Hook arrive at Regina's coronation with their infant daughter, as they enter the room, Hook is holding a doll and not a real baby. (00:38:25)
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.