As the principal is introducing him to his class, Billy Forrester's name appears on the blackboard behind him before he writes it there.
Handwriting of "Billy Forrester" on the blackboard changes between scenes.
After Billy eats the "Barfmallow", the white goo on his mouth and hands appears and disappears as he jumps around.
After worm explodes in microwave, its guts splatter on the glass, and then disappear in next shot.
When Billy is brushing his teeth, and his Dad comes and asks him to watch Woody for the day, the toothpaste in his mouth switches from toothpaste to no toothpaste.
After eating the spicy worm at Twitch's house, all the boys are waiting outside and Twitch runs out, slams the door, turns the lock and says: "No more cooking in my house!" Doors don't lock from the outside.
The bird shown pulling the worm from the lawn is a Pied Crow, an African species. It is not at all native to America.