Other mistake: When Nebbercracker is on the stretcher and is being wheeled away, the grass pulls off one of the last wheels. When the stretcher is loaded into the ambulance both of the back wheels are intact.
Continuity mistake: When the little girl is riding on her tricycle past the monster house there is one "keep away" sign on the lawn. When DJ and Chowder first walk up to the monster house a second sign has appeared.