at the begining of the even Stevens episode

the easy crier Louis is running in the hall and you can see his papers from his backpack are flying everywhere

and if you look closely you can see that Louis had sort of an open red sack instead of a regular backpack but in they exact same shot you then see he had a normal closed red and black backpack it's not that big of a deal but I've watched this episode lots of times and never noticed it.