Continuity mistake: At the beginning when Beethoven was a puppy, the puppy switches are very noticeable. Especially when Beethoven is making his way to the Newtons' house, the colours of each puppy the film makers use for each scene are very easy to tell apart.
Continuity mistake: In the scene where the robbers were told to destroy all the evidence, they are throwing boxes of papers into a giant stove/inferno. When the scene begins you can see fire and smoke coming from the top of the pipe. A couple scenes later when the Newton family (who is following the vet) pulls up to the same factory, there is no fire or smoke coming out.
Revealing mistake: In the shot where Beethoven slobbers on the father's pants during the breakfast scene, you can see him pressing Beethoven's head against his pants, causing the "accident".
Factual error: There's a scene where two of the children are playing a video game. They're both holding controllers and talking as if they're both playing at the same time. But the game they're playing is "StarTropics" for the NES, which is a one-player only game.
Continuity mistake: When the family is eating breakfast, Beethoven steals bacon off of a plate on the table. Before he steals it, there are 3 pieces of bacon, then the camera fades off of the bacon and then back on. There are only 2 pieces of bacon on the plate then.