Other mistake: In the end credits, Michael Coleman, who plays Happy, is wrongly billed as "Micahel Coleman." (00:41:00)
Other mistake: At the end of the episode, when Aurora tells Emma and Snow about Henry in her dream, she says that he said his name was Henry, but he never said his name. He just said, "Don't be scared."
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 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 Regina tells Hook about the dark curse, as she says "This new realm", her arm is hanging down by her side. In the next shot, her arm is bent. (00:03:45)
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: 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 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: After Regina places a rose on Cora's body, the position of the green leaves repeatedly changes between shots. (00:22:05)
Continuity mistake: During the showdown at Lake Nostos, Mulan's long ponytail alternates between hanging down her back to being in front of her shoulder between shots. Emma's hair also keeps changing position. (00:27:30)
Continuity mistake: At Lake Nostos, the pendant on one of Emma's necklaces alternates between being hidden behind her neck (under her jacket) and being visible on her chest. This is seen, for example, when Cora fails at ripping her heart out. (00:27:45)
Continuity mistake: During Emma's sword fight with Hook, when Emma is on the ground, reaching for her sword, Hook sticks his own sword into the sand so that he can drag her away from her weapon. Cuts to a different shot, and his sword is lying on the ground, near his feet. A couple of shots later, the sword is planted in the ground again. (00:27:55)
Continuity mistake: During the battle at Lake Nostos, after Emma lunges at Hook and he flips her to the ground, the amount of dirt on her clothes repeatedly changes. (00:28:00)
Continuity mistake: After Hook throws the satchel that holds Aurora's heart to Mulan, the way she holds the satchel keeps changing; most noticeably, in some shots, she's holding it by the straps, in others, the satchel is lying in her hand. (00:28:20)
Audio problem: At Lake Nostos, when Mulan gives her magical sword to Mary Margaret, in the shot before she says "It deflects her magic", you can se her jaw moving as if she's talking, but nothing is heard. (00:28:40)
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)
Continuity mistake: When Mary Margaret and Emma attack Cora, she vanishes into thin air. In the next shot, they run toward the portal, and their weapons have mysteriously disappeared. They were there in the previous shot, and there was no time to get rid of them, especially not Mary Margaret's quiver, which was strapped to her body. (00:30:50)
Continuity mistake: At Lake Nostos, in the first shot of Emma, Snow and Mulan, there is a giant rock on their left. None of them move, but two shots later, the rock is on their right.
Continuity mistake: At Lake Nostos, when Emma says "You're not going anywhere. This portal's taking us home", in the wideshot, Snow's quiver strap is over her pink cardigan. In the close-up, it is under the cardigan. In addition, Mulan's and Snow's weapons are held at different angles between shots.
Continuity mistake: When Emma and Henry are having breakfast at Granny's Diner, the spoon in the empty cup next to Henry's plate (on his left) changes position between camera angles. In the same scene, Emma's right hand alternates between resting on the table, and picking at her food. (00:13:45)
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.