Continuity mistake: When Emma is trapped inside the cell and is gripping the bars while talking to Hook, she's holding different bars between shots. This happens several times. (00:14:50)
Continuity mistake: Right before Emma and the other women get trapped inside the cell, Emma is reading the scroll left by Rumplestiltskin. The way she holds the paper keeps changing between shots. (00:13:40)
Continuity mistake: When Hook attempts to rip Cora's heart out, as he pulls his hook out of her chest, the hook is pointing downwards. In the next shot, it is pointed to the right. (00:12:55)
Continuity mistake: When Hook kills Regina's guards, the first guard can be seen collapsing. Cuts to an overhead shot, and he collapses again. (00:00:50)
Continuity mistake: When Anita lies dying, Red Riding Hood holds her hand over her mother's chest, in front of the arrow, and Anita grabs her hand. In the next shot, their hands are down at Anita's side, behind the arrow. (00:31:10)
Continuity mistake: In the scene where Albert Spencer burns Jefferson's hat, Ruby's hair alternates between hanging down the side of her face and being tucked behind her ear. (00:35:25)
Continuity mistake: When Hook has climbed down the Beanstalk and is greeted by Cora in the rain, the wet hair plastered to his forehead changes throughout the scene. (00:00:30)
Continuity mistake: When Albert Spencer confronts David at Granny's, Henry's coffee cup moves to a different part of the table, and back again, between shots. (00:04:40)
The Doctor - S2-E5
Continuity mistake: When Regina is in the stable with Daniel, after she says "No, I won't lose you again", in some shot, she has her hands on his face/neck. In others, her hands are on his shoulders. (00:31:45)
The Doctor - S2-E5
Continuity mistake: When Hook is tied to the tree, the arrangement of the ropes changes throughout the scene. (00:24:40)
The Doctor - S2-E5
Continuity mistake: When the women find Hook under a pile of dead refugees, the amount and position of the dirt on his face changes a couple of times. The scarf around his neck also changes position. (00:01:40)
Continuity mistake: At the beginning of the episode, when Emma and Mary Margaret are walking through the camp with a group of refugees, in the first shot, they're at the edge of the camp. Cuts to a different shot, and the group have moved to a different part of the camp and are situated next to a table, before they walk over to a shed. In the next shot, they are farther away from the shed. When it cuts, they are standing next to it again. (00:05:00)
Continuity mistake: When Milah and Killian board The Jolly Roger, as Milah says "Fetch some water", a pirate with a coil of rope around his arm has just ascended the deck and is seen near the steps. In the next shot, he is nowhere near that area (he can briefly be glimpsed as he disappears behind a mast in the lower left hand corner). (00:25:45)
Continuity mistake: When David and Rumplestiltskin walk down the streets of Storybrooke while searching for Belle, as David says "There is a difference between literal truth and honesty of the heart", a car is seen driving through the street. In the next shot, it's gone. (00:21:20)
Continuity mistake: When David and Rumplestiltskin are looking for Belle, when Rumple says "Look, can I ask you a question?", in the background, a man and a woman are crossing the street. In the next shot, they cross the street again. (00:20:40)
Continuity mistake: When Rumpelstiltskin and David are out looking for Belle, they cross the street, and for the rest of the scene, the pedestrians change from shot to shot. (00:20:55)
Continuity mistake: At Granny's, when Belle and Ruby chat, the slice of lemon and the straw in Belle's iced tea move around between different camera angles. The same thing happens to the straw in the half empty glass in front of her. (00:12:15)
We Are Both - S2-E2
Continuity mistake: After Mary Margaret is knocked out by Mulan and falls to the ground, the amount of straws and dirt on her clothes changes between shots. When she is thrown into the dungeon with Emma, her clothes are clean. (00:39:55)
Continuity mistake: After Prince Philip's body is placed on the bier, Mulan wraps the wraith's medallion in a bag and gives it to Aurora. In the wide shot, the strings on the bag are hanging over the left side of Mulan's hand. In the close-up, they are hanging down the right side. (00:33:25)
Continuity mistake: In the scene where Mulan and Aurora are alone in the forest and Mulan is trying to make a fire, she alternates between wearing her long ponytail over one shoulder, and letting it hang down her back. (00:24:45)
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.