Continuity mistake: After Mrs. Russo puts Justin and Max in the lair, she is wondering if she should put the big lock on the door or not. She decides not to and puts the lock down on the counter. Two shots later you see the lock is back on the door, but unlocked. You never see Mrs. Russo put the lock on the door.
Continuity mistake: In the episode "First Kiss," Justin has a girlfriend, Miranda. But in this episode Justin starts dating this new girl from his class, who's actually the same Miranda. This doesn't make any sense. How is she a new student and how could they just meet if they were dating eight episodes ago?
Continuity mistake: When Alex spills a little chocolate, there should be a small puddle at her feet. But in the next shot, there is chocolate stretching right to the other side of the room. There is no way that the chocolate could have spread that far.
Continuity mistake: When Harper makes all the apples fall down, there is one more left on the stand. When it switches to Alex and then switches back to the stand, there are no apples on it. In the next shot the one single apple has reappeared back on the stand, then disappears again in the next shot.
Continuity mistake: When Alex's mother is telling Alex that she can help Grandma with the chickens during the summer, she tosses Alex's hair back and we can only see Alex's back with the hair. When the camera pans immediately after, it shows Alex's face and her hair back where it was before her mother moved it.