Go to the part in the lunchroom, where Peter uses his web by accident. The web clings onto a tray with food in it. Peter flings the web back and the tray hits the person behind him. All the food got on him. After the lunchroom scene, Peter is at his locker. Then the person who had the food on him tried to punch Peter. If you look at the person's back, there is no food! I wonder how he cleaned himself so quick and made the shirt look brand new!