Other mistake: When Greg is looking at the video of Rowley sitting on the foil ball, he notices it has only 4 views on YouTube. However, if you look closely, it has 24,963 comments - impossible if it's only been viewed 4 times.
Suggested correction: YouTube is broken. This kind of thing actually does happen in real life quite frequently. In fact, a video I was just watching had that problem.
Continuity mistake: When visiting grandpa, Rodrick is given a glass of milk. He takes a large gulp and theatrically spits over Greg, soaking his shirt, but then they cut back to the glass on the table and there is still the same amount of milk in it.
Continuity mistake: At the end of the movie, Rodrick is driving Greg to school in his van. There is a close-up showing three flyers beautifully arranged on the top of the dashboard as they are driving along, and a soft toy. After Rodrick pulls away, there is no sign of the flyers and soft toy.
Continuity mistake: In the scene where Susan's editors come round for supper, Greg and Rodrick have to return home by 9pm. And they do, as there is a lingering close-up of the wall clock in the sitting room showing the time as 20.55, and dialogue centring on this [i.e. the clock has not stopped]. There is then a lot of commotion about whether Susan's column is a wholly accurate depiction of the dynamics of the family that takes a good couple of minutes to play out. The editors make their excuses and leave, and we see the clock again as they are leaving, but in all the time this has taken the clock has not advanced. Then there is a further scene where the boys argue in the front room and after that has played out we see the clock again, and time has continued to stand still.
Continuity mistake: When Rodrick spits milk at Greg as Greg is reading the joke card, in the bottom right Rodrick is picking up the glass of milk ready to drink it and spit it at Greg. But as the camera switches angles, Rodrick is picking up the glass of milk again. (01:13:45)
Continuity mistake: When Rodrick spits milk at Greg, we see Rodrick about to spit milk at him. In the background, behind the glass, there is no one walking on the pavement. In the close-up shot of Rodrick spitting the milk, there are multiple people walking on the pavement. This is all very fast and can be easy to miss.
Visible crew/equipment: When Greg has arrived at church, and he gets out the car he realises he's been sitting on some chocolate. When Greg's dad is trying to clean this off Greg's trousers and the camera pans upwards, the reflection of a cameraman can be seen in the window of the car. (00:24:32)
Other mistake: After Greg gets beaten up by the party girls, it cuts to a page in the book where Rodrick is giving Greg and Rowley drum lessons. Although the doodle Rowley is smiling in this shot, he is actually frowning in the book.
Continuity mistake: When the students are laughing at the paper Greg read, Patty says "Loser," then cuts to Holly laughing; Fregley is laughing in the background in both shots. Between shots, his head changes positions and his mouth opens wider.
Continuity mistake: Chirag Gupta is not standing on a stool whilst painting at the beginning, but then moments later he steps down from a stool to greet Greg Heffley. (01:02:30)
Audio problem: When Rowley says "how are they not going to notice the lock's gone?" his lips don't move.
Continuity mistake: After Rowley's magic show, Holly goes backstage to talk to Greg, but in the scene of Rodrick playing the drums, Holly is back in her seat in a matter of seconds.
Continuity mistake: Greg tosses the foil ball onto his bed and it lands near the center of it. However when Rowley accidentally sits on it, the ball is closer to the edge.
