When Gillespie takes Virgil to the morgue to inspect the body, Virgil notes that the time is 4:45 am 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 appears more like late morning.
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 gentleman on the sidewalk . He is dressed in a shabby suit, a beige V-neck sweater, and a hat. The car then drives 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.
When Tibbs and Endicott slap each other, in the wide shot, Gillespie can be seen standing up. But, in the close-ups of the Chief, he remains resting on his elbow, and then stands up when they're done.
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.
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 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.
When the Sheriff picks up the phone, which has multiple lights for different lines, the light does not light up.
The film depicts a Missouri Pacific train running through Mississippi, which never had a route there.
Can't help but wonder why a black man in a suit appears comfortable while locals - white southerners - are sweating in short-sleeve shirts.
As Tibbs examines the body in the morgue, he states that the time of death is measured by heat loss in the brain; it's actually the liver temperature that is used for such determinations.
Liver temperature is now routinely used in determining time of death but, in the 60s, there were various other indicators used, including brain temperature.
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. However, this is not a Goof as it could just be a broken clock or even a barometer (with a smaller humidity gauge below it).
The police chase Harvey Oberst through the yellow leaves of an autumn forest, clearly indicating that it is not the middle of summer, as claimed in the movie.
It's still early morning when Harvey Oberst is running for Arkansas. (Tibbs wants to catch the noon train.) On the bridge, the sun should be on his back, not his face.
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.
It's supposed to be a very hot summer, yet Mrs. Colbert and Chief Gillespie are walking around in a coat and a jacket.
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.
Mr. Tibbs inspects Mr. Colbert's car for evidence. The car is a 1967 Lincoln Continental convertible, the model year indicated by the "flowerpot" impact absorbing module in the center of the steering wheel, a feature only seen on 1967 Ford products. However, the film takes place in the summer of 1966. 1967 models did not go on sale until September of 1966.
When Harvey is being chased through the woods, there are shots from Harvey's POV as he looks around the woods. Looking at the bottom of the screen where Harvey's shadow should be, his shadow is that of the cameraman with the camera mounted on the shoulder.
In the final scene when Gillespie puts Tibbs on the train, the shadow of the boom microphone can be seen on the station house.
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.
When all three men, Virgil, Sam, and Police Chief Bill go into the diner, Virgil's breath can be seen. Although the film is set in warm, humid Mississippi, it was filmed in chillier Illinois.
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. Also several characters exhale vapor visually and contradict the film's title.
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.
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.
Mrs. Colbert tells Virgil that her husband left their hotel room late that night because he couldn't sleep. But when he's found murdered in the street he's wearing a complete suit and tie, with dress shoes and socks. This would mean he had completely re-dressed himself in day-wear just to go out for a walk at 11pm.
Delores is supposed to be alone at home while her brother is working at night, but when Sam is driving away after watching her, the shadow in the window is a man.
Following Delores Purdy's rape accusation, Gillespie asks Deputy Courtney to come in with a pencil and paper but his brother Harold enters the room instead.