When people are shown going onto the Mississippi River bridge, there is an Arkansas highway sign, something that would not have been seen on the Mississippi side of the river.
It's still early morning when Harvey Oberst is running for Arkansas (Tibbs wants to catch the noon train). The sun should be on his back, not his face on the bridge.
When the sheriff is called to go and see the Mayor at his place of work, Gillespie drives through Sparta and passes an elderly black gentlemen on the sidewalk . He is dressed in a shabby suit wearing a beige V-neck sweater and a hat. You then see the car drive a few hundred yards further into town and in the next shot, a few seconds later the same man is again walking along the sidewalk.
The action is set in the heat of a Mississippi summer, but cotton pickers toil in the fields. That's done in late fall, never in the summer.
While inspecting the body in the morgue, Tibbs inspects the left hand and after placing the hand down the body takes a short breath of air.
When Chief Gillespie keeps Virgil at his house they appear to be drinking a bottle of Wild Turkey bourbon. When the Chief gets up and walks out of the room the bottle is not on the table. This occurs just after the Chief tells Mr. Tibbs that he doesn't want his pity.
The police chase Harvey Oberst through the yellow leaves of an Autumn forest, clearly indicating it is not the middle of summer, as claimed in the movie.
Calendars in diner and sheriff's office differ by many months.
When Harvey is being chased through the woods, there are shots from Harvey's POV as he looks around the woods. If you look at the bottom of the screen where you're supposed to see Harvey's shadow, his shadow is that of the cameraman with the camera clearly mounted on the shoulder.
When Virgil is in the morgue helping examine the corpse, the clock on the wall stays on the same time throughout the discussions and examinations.
When Gillespie takes Virgil to the morgue to inspect the body, Virgil notes that the time is 4:45am in trying to determine the time of death. Gillespie gets a call that they're tracking a suspect and he leaves the morgue immediately. The next shot shows Harvey running through the woods and then Gillespie in his car waiting to apprehend Harvey. He is wearing his sunglasses. It shouldn't be any later than 5 am but the sun is up high and it's appears more like late morning.
It's supposed to be a very hot summer, yet Mrs. Colbert and Chief Gillespie are walking around in a coat and a jacket.
When all three men, Virgil, Sam, and Police Chief Bill go into the diner, we see Virgil's breath. Although the film is set in warm, humid Mississippi, it was filmed in chillier Illinois.
Delores' brother is shot and falls on his back. His body is in line with the car, his head near the driver's side front wheel. In the second shot his head is near the license plate. In the third shot his body has changed position and is perpendicular to the car parallel to the bumper.
When Det. Virgil Tibbs is at the train station, and Police Chief Bill Gillespie comes back to get him, in the wide shot there is a dog slinking along the building. When they close in, the dog is gone.
The town of Sparta is in east-central Mississippi. The Mississippi River forms the western border for most of that state. If Harvey Oberst (the fugitive being chased early in the film) made it as far as a bridge to Arkansas, he would have been at least 100 miles out of the jurisdiction of the Sparta police (who catch him). Even if, unbeknownst to the audience, the Sparta police had been deputized by some other jurisdiction, it's doubtful that they could have brought him back to the Sparta jail in the time frame presented.
Though the film takes place during a Mississippi summer, the exhaust of the patrol car can be seen briefly as condensed vapor as they drive up to Endicott's house. The only way this would be possible in the daytime is if the temperature outside was cold, which it was because the film was actually shot in Illinois during the fall.
Sam apprehends Virgil at the train station and takes him to the Police Station. As they approach the entrance both the inside and outside doors are closed.The inside shot of them entering the station has only the screen door closed. The inside door is open.
When the fugitive jumps down the embankment after crossing the tracks the man's head disappears just before he fully gets down the embankment.
In the initial scenes shot in the Sparta police station, veteran character actor Peter Whitney is established as the policeman named Courtney. The interaction between characters Gillespie and Courtney throughout the film reinforces this, but near the end of the film, for whatever reason, an inexplicable change in characters takes place. Right after the young girl, Deloris Purdy gives her account of her cemetery encounter with Officer Sam Woods and confirms that she is pregnant, Chief Gillespie calls out, "Courtney, you'd better get in here with a pad and a pencil..." Almost immediately, actor William Watson, who played Officer McNeil in the story enters the room ready to take notes... not the 'Courtney' we expected to see.
It happened once more at the conclusion of the confession scene when we see Ralph speaking into the tape recorder microphone held by Officer McNeil... "That's all... I didn't mean to kill him..." After a momentary pause, Chief Gillespie steps forward and says, "Yeah... alright Courtney, that's enough." How and why did William Watson become Courtney?
When Sam Wood first approaches the train depot, he casts a very long shadow reaching behind him all the way up the building wall as if lighting is directly in front of him. In the next shot when he is passing the door and sees Virgil, the shadow has greatly shrunk down as if the lighting is directly overhead.
The lyrics to the song Sam listens to on his transistor radio describe a bow-legged Polly and a knock-kneed Paul not being able to get together, yet anatomically these would in fact be ideal physical characteristics for a guy and a gal to "get together".
In Gillespie's first scene he is trying to get the air conditioner to blow harder in his office. He reaches up and gives the knob a good sized turn, only when his hand pulls back the knob is still in it's original position.
After Wood tosses Tibbs' wallet on Gillespie's desk, the pattern of the money sticking out of it changes several times between shots.
When Virgil enters Mama Caleba's shop, the cardboard product display on the counter is facing toward the front door. When Mama appears from the rear to engage with Virgil, the counter display has shifted, now facing the rear.
The film depicts a Missouri Pacific train running through Mississippi, which never had a route there.
It would have been impossible for Tibbs to ride a Gulf, Mobile & Ohio passenger train in Mississippi at the time the film depicts. The GM&O had discontinued all passenger service south of St Louis in the 1950s.
When Harvey is running onto the bridge, the route sign says Arkansas 49. Arkansas does not have a State route 49. There is however a U.S. Route 49 that crosses the Mississippi River from Mississippi into Arkansas.
In the final scene when Gillespie puts Tibbs on the train, the shadow of the boom microphone can be seen on the station house.