Tallahassee - S2-E6
Revealing mistake: When Neal is being chased by August, he runs on top of a car before attempting to jump the fence. Just before he jumps on top of the car, you can see that the one who actually performs this action is Michael Raymond James' stunt double. (00:26:40)
Revealing mistake: Hook's wire is visible as he climbs in Rapunzel's castle. (00:10:05)
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: 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)
Unforgiven - S4-E13
Revealing mistake: When Snow White and Prince Charming arrive home at the Royal Castle on horseback, you can easily see that the ones riding are not Ginnifer Goodwin and Josh Dallas, but their stunt doubles. (00:02:55)
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)
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: 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 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)
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 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: 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)
Welcome to Storybrooke - S2-E17
Revealing mistake: After Regina burns the curse that will make Henry think he loves her, when Henry walks over to Emma and the others a few shots later, Regina has the curse scroll in her hand again. (00:36:40)
Revealing mistake: As Moe French steps out of his florist's van, he is greeted by Mr. Gold and his lackey. As. Gold says, "Well, this is just perfect", in the background, you can see the clock tower building, but without the clock tower (the actual clock tower is CGI). (00:03:50)
Revealing mistake: When Hook is down in the pit, trying to escape the undead Maleficent, after he says, "Maleficent. Love you in earth tones", there is a wide shot of Hook and Maleficent where you can see the face of Colin O'Donoghue's stunt double. The stunt double's face can also be seen in the shot where Hook stands up after climbing on top of the rock. (00:22:20)
Revealing mistake: Ruth has gray, curly hair. When Bo Peep bangs The Shepherd's crook on the ground, sending Ruth and David flying to the ground, in the shot from behind them, Ruth's hair is much smoother; the one falling is obviously Gabrielle Rose's stunt double.
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.