Continuity: When George goes out to get the newspaper, the shadow of the house is only half-way across the lawn. But when he comes back seconds later, the shadow is all the way out on the sidewalk.
Revealing mistakes: When Beethoven dragged the table and George's obnoxious clients at the sidewalk down the street, the table had "skis" on it.
Continuity: When Alice places bacon on George's plate, she puts down two. Before Beethoven eats one, there are three. This is because the same footage of bacon being placed a plate was used twice (which had two pieces).
Continuity: When the dog comes into the kitchen he gives the mail to Alice, and she puts it under her arm. In the next shot, Alice is putting bacon on Ryce's plate and the mail is not under her arm.
Continuity: In the scene after Beethoven "attacks" the vet, Dad goes into the backyard and gets Beethoven to take him to the vet's office, the dog's neck and snout are mysteriously clean even though only moments earlier they were smeared with fake blood.
Continuity: When the vet gets the bullets to the gun, it is said that the bullets will explode on contact. Well, when the gun is shot later on in the movie, the bullet does not explode.
Continuity: After Brie knocks over her glass at the barbecue, Alice picks it up, and it's intact. When she walks away with it, it's broken.