When Matt arrives at band camp he is wearing black and white shoes. When he places his bag down he still has the same color on. In the next shot when he climbs underneath the wooden fence to go and see what all the commotion is about, he is wearing white sneakers.
When Matt is in the pool, his hair switches back and forth between wet and dry.
When East Great Falls is celebrating after Stiffler beats Brandon in the duel, Oscar goes to take a seat twice. Stiffler and Ernie are sitting at the picnic table and Oscar takes a seat next to Stiffler. Then the camera cuts to a close up of Stiffler and Oscar is taking a seat again.
In the final scene of the movie where the band is playing at Robard's, Matt's bagpipes constantly change from being held in his hands to laying on the ground. Notice Matt using his hands to make gestures but the camera will show that the bagpipes are in his hand, and then a second later the bagpipes will be on the ground etc.
The shoe that Elyse takes off at Robards appears back on her feet after she finishes composing the band's music.
The "oboe" used in the movie is actually a cor anglais.
In the movie Matt marches, playing a Triangle. The Triangle is actually not marched on the field, but played in the pit (front ensemble).
In the movie Matt uses an Apple PowerBook and an Apple Desktop.
Mac OS X has the close window/minimize/maximize buttons in the top left; but in the film, they are on the top right.
When Elyse is serving herself some grape juice, it's completely transparent, just like water.
After the curtain was ripped off, it shows Elyse standing with her music stand on the ground. When Matt turns and shows Elyse again, the music stand is standing back up.
When Stifler is adding Ipecac to the grape juice you can see Oscar standing in the background watching Stifler minutes before he approaches and chases him away.
The postcard Matt receives from his brother is addressed to East Great Falls, MI 07720. That ZIP code is actually located in Bradley Beach, NJ.
When Stiffler is in the nursing room for getting toothpaste up his nose, the shadow of a boom mic can be seen over the bed for about a second.
When Chloe and Ernie are in the bedroom Chloe says she has 6 piercings not including the ones on her face she actually has 7 piercings, she missed out her belly button piercing. In an earlier scene when they are playing the quiz when she removes her shirt her belly button piercing is clearly visible.
When Stifler first discovers the robot, Ernie tells him he wants to someday work for NASA. When Ernie explains the NASA acronym, he defines the S and A as Space Association, but it is really Space Administration.