Continuity mistake: The glass that was dropped and shattered on the floor had a different pattern of fragments when Mitch [Robin Williams] knelt to clean it up. Most obvious was that the majority of shattered pieces settled toward Mitch's feet but were on the opposite side of the largest piece of glass during clean-up. There's also a "stupidity" in the way Mitch wiped up the glass - pressing down on the thin towel (apparently to entrap fragments), which is most likely to result in getting pierced. (00:01:40)
Continuity mistake: During the early part of the movie, the left rear door of Doc's car is dented. For the rest of the movie, the dent is gone.