Continuity mistake: In the episode with Alex at the art museum and Justin a teacher's assistant, as Alex is in the room with all the paintings, she puts a piece of rope around the door handles. Later on when Alex says, "Go ahead scream panic," we see Alex in front of the door, but the rope is gone, but the next time it shows Alex the rope is there again.
Continuity mistake: In the "Wizards vs. Werewolves" special, just as the Russos learn that Alex and Mason have gone to Transylvania, Max is playing on his Nintendo DS. He then flips it shut. The shot switches to Justin, Jerry and Teresa. They talk and the shot switches Back to Max, and you see him flip the Nintedo DS shut again.
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 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.
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: 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: 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: They learn the miriana animata (make an inanimate object come alive/walk/talk) but in episode 10 they already learned this one. Alex made Justin's pimple come to life (EP 10), so why was she so confused in EP 19 about how if it gets feelings, she can't make Manny the mannequin inanimate again? Her, Max and Justin (to an extent) made it as though they never learned this one or had troubles with this spell.
Continuity mistake: After Justin and Juliet come back from the movie, they sit down in front of the sub station. When Justin and Juliet talk, look at Juliet's left shoulder; her sweater goes from being on her shoulder to slightly off her shoulder every time the camera pans back and forth on them.
Continuity mistake: As Justin comes hysterically in to the restaurant from the lair, he runs over by the door to pull the shades down. A few seconds later when the camera is on Alex, you can see one of the shades is on the ground, However, after Alex says "you turned in your girlfriend to the Monster Hunter council" and Justin is shown, you can see that the shade has been put back in place.
Continuity mistake: In the mummy episode, Juliet states that sunlight kills her. However, in the episode before that (Three Monsters), she is shown walking into the sub shop with a calzone box during the day.
Continuity mistake: Alex's hair in season 3 changes back and forth between her shoulder length Bob and her long curly hair. The first instance of this is in the first episode with Mason in it. She had short hair in the previous episode, then it's long and curly in this episode, and then the following episode it's short again. This happens many times in season 3.