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)
Snow Drifts - S3-E21
Audio problem: As past Hook carries Emma aboard his ship, he drunkenly and loudly declares, "Behold! The Rolly Joger." Although they are several meters away from the camera, you can see that his lips are barely moving. (00:32:15)
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.