When Billy is in the first grade, he is making a snowman. All the other students are making perfect looking snowmen with cotton balls, but Billy's is nothing but a huge mess of cotton balls, construction paper, and paste. It looks nothing like a snowman. However, when Billy is outside of school and is putting the moves on one of his classmate's moms, his teacher, Miss Lippy, brings out all his stuff from class that day, including his snowman, which now looks absolutely perfect.
In the scene where he has to write in cursive the words change shape as though they wrote it a few times making the scene. It's around the time he is throwing the fit.
In the part where he is putting water on his pants because its cool, the water pours out. But the kid before him had to keep pumping to get water out.
When Billy, Norm MacDonald, and that other guy throw pickles at the fast-food restaurant window to see which one will slide down the fastest, the pickles' respective positions on the window change significantly from when they're thrown to when the actual "race" is occurring. The position then changes again after the race is over and the pickles are still visible in the background.
After chasing the penguin, his shirt is unbuttoned and he falls. When Wanita pulls him off the ground and tells him to get dressed, his shirt is buttoned.
When Billy is on the bus and the kid dares him to touch Ms. Vaughn's boob, when the camera is looking at the back of Billy's head, you can see in the background that Ms. Vaughn is 3 seats in front of him. Then after he tries to grab her and goes back to sit back down his seat is only 2 seats back.
When the O'Doyles are in the car, don't you think that they would know that they are falling off a cliff?