Tallahassee - S2-E6
Continuity mistake: When Anton throws the compass to Emma, the compass changes position on the floor between shots, seen from the lines/cracks in the floor. (00:33:45)
The Doctor - S2-E5
Continuity mistake: When Emma is questioning Hook while the group is gathered around the bench, the folds in the cloth/bundle lying on the bench keep changing between shots. (00:14:30)
Continuity mistake: While Emma is talking to Mary Margaret on the phone, an extra (lady with a purple shopping bag) comes from behind Emma. The scene then switches to Mary Margaret, then back to Emma, and we see the exact same extra walking behind her again. (00:14:40)
Continuity mistake: After Charming gives Rumpelstiltskin his cloak, the cloak keeps changing position on Rumpelstiltskin's table. (00:22:05)
Continuity mistake: When Mary Margaret and Henry are being teleported out of Granny's Diner by Nimue, they aren't wearing any outdoor clothing. However, when they emerge at the pond with the others, Henry is wearing a jacket, and Mary Margaret wears a coat and a scarf.
Continuity mistake: As Ashley tries to break into Mr. Gold's safe, which is hidden behind a painting, in the first shot, she's moving the painting with her left hand. In the next shot, her right hand is up by the painting, and the lever on the safe has changed position, even though there was no time to turn it. (00:09:55)
Continuity mistake: When Elsa is walking down the middle of the street through Storybrooke, she is leaving a trail of ice on the road behind her. Shortly after seeing a wedding dress in a store window, she walks towards the store, and the trail of ice behind her is gone. (00:07:00 - 00:07:35)
Snow Drifts - S3-E21
Continuity mistake: When Emma changes clothes in the Enchanted Forest, as she puts on gloves, in the wide shot, she begins to put the glove on her left hand. In the following close-up, her left hand is bare, and she's putting the glove on her right hand. (00:18:15)
Continuity mistake: When Zelena loses the Dark One's Dagger, it lands on the ground, the patterned side of the blade facing upwards. When Regina picks up the dagger, the patterned side is facing downwards. (00:28:10 - 00:29:20)
It's Not Easy Being Green - S3-E16
Continuity mistake: When Hook is at the beach with Henry, after he says to him, "Fair enough, mate", the pendant on Hook's necklace goes from resting against his chest, to being partially tucked under his waistcoat. In the close-ups, the pendant is completely covered by the waistcoat. (00:26:50)
Continuity mistake: On the plane, Henry is eating baked goods from Cinnabon's. The size and position of the stains of frosting inside the box changes after he says "The only thing that could make this day any better, is more frosting." (00:40:25)
And Straight on Till Morning - S2-E22
Continuity mistake: When Baelfire is getting ready to leave The Jolly Roger, his right hand, which is holding onto the sack he carries behind his back, keeps moving up/down between shots. (00:29:15)
And Straight on Till Morning - S2-E22
Continuity mistake: In the scene where Mr. Smee asks Hook why Baelfire is still aboard The Jolly Roger, when Hook says "Anyone who disobeys can walk the plank and pray the mermaids take pity on his soul", as he begins to walk down the steps, Smee is several meters away from that area, with his back turned (look behind the mast). In the next shot, he is much closer to the steps, and is facing the viewer. (00:26:20)
And Straight on Till Morning - S2-E22
Continuity mistake: At the beginning of the scene where Baelfire confronts Hook about Milah, when Hook is talking to Smee, the hair on his forehead keeps changing between consecutive shots. (00:25:55)
Continuity mistake: When Belle is looking for Baelfire's shawl and distractedly sets down the gun, the gun keeps changing position on the bench. (00:24:00)
Continuity mistake: When Killian rallies his crew to join him in taking over the ship and becoming pirates, as he's holding onto the ropes used to control the vessel's sails, the number of ropes he's grasping repeatedly changes between shots; in some shots, it's only two ropes, in other shots, there are three ropes in his hand. (00:38:50)
Going Home - S3-E11
Continuity mistake: In the Neverland flashback, when Hook offers Tinker Bell the rum bottle, the stopper (attached to the bottle) is hanging over the back of his hand. In the next shot, it is not. (00:09:55)
Save Henry - S3-E9
Continuity mistake: When Regina talks to Rumplestiltskin, he is holding onto the bars in his cell. In the beginning of the scene, his left hand keeps clutching different bars between shots. After Regina says "Nothing can stop me now", his hands keep going from holding the bars and not holding them. (00:02:00)
Continuity mistake: In Neverland, the piece of cake that Rumplestiltskin wishes for changes during this scene, with regard to the amount of chocolate, white cream, etc, and also its position on the wood after Rumple puts it down. (00:16:45)
True North - S1-E9
Continuity mistake: When Emma and Mary Margaret are conversing on the bed, Emma's sweater moves up/down her left shoulder several times. For example, as Emma says "Apparently that book you gave him, aren't exactly the stories in the most traditional sense", the sweater is over her shoulder. In the next shot, it's off her shoulder. In the following shot, it's covering her shoulder again. (00:37:45)
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.