Tallahassee - S2-E6
Continuity mistake: When Emma is arrested, she has a flower tattoo on her left wrist. When she's climbing the beanstalk with Hook, in a few shots, her wrist is bare, and you can see that the tattoo is missing; this happens, for example, when she remarks, "You should be used to people not trusting you." (00:09:10 - 00:29:30)
Tallahassee - S2-E6
Continuity mistake: In the giant's treasure room, there are many giant gold coins near the skeleton of Jack the Giant Killer. The amount and position of the coins repeatedly changes. For example, when they find the skeleton, there are several coins on the edge of a small dais, but when Emma saves Hook from the trip wire, they are missing. (00:24:40)
Continuity mistake: At Lake Nostos, when Emma is pinned down by Hook, the ground beneath her changes between shots, with regards to the markings in the sand (from the fight), as well as the amount of stones, twigs etc. (00:29:00)
The Miller's Daughter - S2-E16
Visible crew/equipment: When Rumpelstiltskin goes to Cora as she is trying on her wedding dress, as he sits down on the chair behind her, you can see the tape used to mark the spot on the floor - it's bright red and in an X shape. (00:24:39)
Continuity mistake: When Red meets Quinn, the way her hood is draped over his arm changes throughout the scene. The same thing happens when Red is holding it afterward. After Quinn drops the hood, the way the garment is crumpled up on the ground changes between shots. (00:12:05)
Continuity mistake: At Granny's, when Ruby is clearing tables and Billy startles her, the amount and position of the food on a plate changes between shots. The cup and the napkins also change position on the table. (00:02:35)
Tallahassee - S2-E6
Continuity mistake: When Hook and Emma find the skeleton of Jack the Giant Killer, in the close-up shot, Jack's sword is in the skeleton's hand. When Emma remarks, "With that toothpick?", the sword is lying beside the hand. When Emma grabs the sword while being chased by the giant, the sword is back in Jack's hand. In addition, the skeleton's arm alternates between being bent and sticking straight out between shots. (00:23:15)
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.