Continuity mistake: In the kitchen, Billy's mom shields her face with a table. A frame later it's at waist level. (00:54:50)
Continuity mistake: When Bill is in the bar drawing a cartoon of Mrs Deagle, the amount of popcorn on the table increases between shots.
Continuity mistake: After Gizmo poops, there's a close-up on Billy's stunned face, perfectly lit. A frame later, from a different angle, the face is in shadows.
Continuity mistake: Both the scene of Billy, Pete, and the science teacher looking at the gremlin cocoon, and later when Pete is in class watching the science film, occur on the same day, yet Pete is wearing different clothes.
Continuity mistake: When Billy smashes the Candy store window the amount of stuff behind the glass changes between shots. (01:27:50)
Answer: The original film was released before the PG-13 rating existed (it was one of the films responsible for its creation). Producers decided to remove some of the language and violence for the DVD release to avoid complaints about the PG rating.