Continuity mistake: When Patrick is singing to Kat, while the band is playing he can be seen dancing behind a girl in a blue shirt sitting down. The camera cuts to the band and back to Patrick when he starts to sing but this time he's near a group of guys who are in front of a red flag. The camera then cuts to Kat and then back to Patrick who is back with the girl in the blue shirt - this time he's next to her rather than behind her. A few seconds later you can catch a glimpse of the girl and the guys both behind Patrick in their same respective spots which are nowhere near each other (the girl being further down from the guys).
Continuity mistake: In the classroom where the students are dissecting frogs, the camera is showing a close up of Cameron and Michael talking and in the background you can see Patrick take out his tool to stab the frog. Then the camera immediately goes to a close up of him and he re-takes out the tool and actually stabs it.