Continuity mistake: Rancer was shoving dinner rolls into his mouth, demonstrating his competitive eating ability/skill. He still had some in his mouth, but after he ran his hand over his mouth, there suddenly was no sign of any food in his mouth. (00:16:10)
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)
Other mistake: The clock on the kitchen wall was at 5:03 PM when Donna asked, "Where the heck can they be?" After an outside scene and returning to the kitchen, the clock was still at 5:03 when Donna said she couldn't find her camera. The battery in the clock could have been dead, but the display time was what could be expected around dinnertime (suggesting the clock was supposed to be in working condition). The "non-advancing" clocks seem to be a common occurrence in movies. (00:10:20 - 00:11:18)
Revealing mistake: The luminaries lining both sides of the driveway were not lit, although there were a few bags that contained a small circle of dim light that gave the impression of being lit. One of the bags was nonetheless able to catch Boyd's pants leg on fire. (00:11:42)