In the flashback from Alex and Harper's point of view, after they run into the sub station, they turn their backs to everyone else and have a brief conversation before Justin yells that Juliet's back. However, earlier when that scene took place, Alex and Harper did not turn around and have that brief conversation. They just stood there at the door in stunned silence looking at everyone else.
In a previous episode of season three named "Marathoner Helper", Alex promised not to use magic on Harper even when Harper asked at the end of the episode, but in this episode Alex casts a spell on Harper to turn her into young Juliet.
Justin looks at pictures of Juliet Van Heusen his Ex-Vampire girlfriend. The problem is vampires cannot be seen in mirrors as shown in previous episodes. Yet how can there be a picture of Juliet Van Heusen when cameras use mirrors to transfer the image to paper.
In the opening segment, after Justin says "swim with dolphins", there's a reaction shot of Alex and Harper. In the background you can see Jake T. Austin (Max) peeking in through the front doors of the sub station.