Continuity mistake: There is no knife on the table when the wife enters the kitchen at the very end, however, she walks straight to Louis, hugs him and then magically a knife appears at the edge of the table which she picks up and uses to stab him (implied - the movie actually ends at that point).
Factual error: While Fletch is riding with the bikers, they stop at a stop sign where a family in a station wagon roll up their windows in fear. A sign at a service center in the background is the Castaic Junction, which is in the greater Los Angeles area. The movie is supposed to be taking place in Louisiana. (01:12:35)
Continuity mistake: In one scene we are looking at a shopping complex known as Greenspring Station which Nina is being chased through. Somehow she winds up being chased through a K-Mart. Anyone familiar with the Baltimore area, where the movie was shot, knows for a fact that there is not a K-Mart anywhere near that ritzy section of town.
Factual error: When Harry is standing on the ceiling fan, the young boy pulls the lever backwards to increase the speed. If you read the side of the lever, you can see that the boy is actually pulling the lever to the slow direction. (00:40:30)
Factual error: After the passenger door gets ripped off the Oldsmobile Toronado, a female voice is heard repeating that the "passenger door is ajar." While the Toronado was available with an optional Voice Alert system, the GM system used a male voice.