In the scene where Bo (Nick Nolte) and Harley (Don Johnson) are talking outside the abandoned house. Harley is standing furthest from the house and has a stick in his hand and tosses it. Then when the girl calls Bo from the window, he is standing closest to the house and still has the stick in his hand.
Near the end of the movie, the black Ford switches from clean to covered in mud several times.
After the '57 Chevy first crashes into the crazy cop's police car, the position of the '57 keeps changing.
Harley spots a white '57 Chevy Convertible on the side of the road and suggests the windows could be used to replace the yellow hardtop's windows. However, this will not work for both windows. The door glass is the same, but the right rear quarter window was also shot out on the yellow hardtop and it has a distinctly different shape than the window on the convertible and won't fit.
When they're escaping the drive-in after Junell gets the money from Tom, Bo cuts off a Chevy Coupe and it crashes into a parked white '57 Chevy Convertible bashing in the trunk. Later, when they are many miles down the road, they steal the windows from a white '57 Chevy Convertible on the side of the road. This is the same car from the earlier crash and it even has the damaged trunk.
The blood on Wittakers coat is bright red, even two days after he got punched in the face. It would have dried and turned dark red.
After the shop owner shoots the glass jar filled with candy, the wires from the explosive charge used are visible.
As "Weird Tom" and his gang are in their car on the search for the film's heroes, one can clearly see various '60s and '70s cars through the rear windshield (the film is set in 1958).
When Bo and Harley are in the small grocery store talking in an aisle, the packaging of all the items on the shelves is from the 1970s, not from when the story supposedly takes place in 1958. For instance, the Hamburger Helper Bo is leaning against wasn't introduced until 1971.
When Harley is staged to race "Weird Tom" and both drivers are revving their engines, we see a late 1960s Sun Super Tach on the dash of Harley's Chevy. The film is set in 1958.
In 1958 highway striping was white. In the film, the center lines are shown yellow. These are the post MUTCD 1971 markings, which had been fully implemented by 1975-6 and were very hard to find before 1973. Because the film is set in 1958 there should be full white striping on the roads.