Continuity mistake: In the scene where Coco tears up the photo of Luke with the women, he tears it carelessly, starting with the upper left corner. The end shot of the movie shows the same photo, reassembled, showing a neat, cross-wise tear, with the center of the tear directly over Luke's heart.
Continuity mistake: In the wide angle shot of Chief Gillespie approaching Virgil Tibbs at the train station, there is a dog on the platform, in between Gillepsie and Tibbs. In the next shot, a closer view of Gillespie approaching Tibbs, the dog is gone.
Revealing mistake: When the farmer is going to shoot the sign the bank put up, you can very well see the mark where the hole is going to appear.
Continuity mistake: There's a scene where Audrey Hepburn's husband Sam is leaving their apartment. Standing on the pavement outside he hails a cab, which pulls up through a (quite sizeable) puddle, splashing him with water. Opposite him on the other side of the road are parked two cars and the villains' Volkswagen van. There's a quick cut-away exchange of "pleasantries" between Sam and the cabby before it drives off. The next shot has the villain (Richard Crenna) emerging from the van, crossing the street, and making for the door to their apartment, only all of a sudden the puddle has disappeared, as have the two cars which were parked behind the Volkswagen van.
Plot hole: At the beginning of the movie, Reese (and Walker) rob from a "drop" at Alcatraz. Reese uses that money to pay off "The Organization." At the end of the movie Brewster tells Walker the only place to get cash is at the drop. "The drop is the same but the location has changed." Brewster receives the money at the drop. This makes it clear the original drop was stealing from "The Organization." Why would Reese be able to pay off "The Organization" by stealing their own money from them?
Factual error: The narrator near the beginning says Al Capone was born in Italy. He was actually born in Brooklyn NY.
Factual error: In the scene when the two criminals are in the hardware store, two vehicles are parked outside that are clearly late 1960's automobiles, despite the film being set in 1959. (00:15:25)
Factual error: When the ambulance arrives the policeman, at the crash scene, is wearing a City of London Police helmet (different from the Met) yet he is in a Metropolitan Police area.
Revealing mistake: Inspector Emil arrives at the morgue; pay attention to the body, just before he asks "You are...?" to Armstrong, the sheet covering the cadaver rises and fall as the departed takes a few deep breaths. (00:32:00)