After the crazy guy rolls the black Plymouth, there is clearly damage to the drivers side roof and the rear wheel on the driver side is bent at an extreme angle and the passenger side rear wheel completely flies off the axle. However, moments later when Thunderbolt and Lightfoot are going down the road, there are no signs of damage.
When Gloria is getting dressed after having sex with Thunderbolt, her bra disappears completely when she puts her dress on.
When Thunderbolt is delivering his sermon in the church, his hair is heavily oiled but it appears quite dry when he emerges from the church, chased by Dunlop.
Lightfoot is wearing the suit that Eddie was killed in, yet there is no visible damage from bullet or blood.
(at around 1h 0 mins) Mario stops by to see the boys, and gets out of his car in a pouring rain storm. The area behind him shows clear blue sky with bright sunshine. Seconds later, it's overcast; still later in the scene it's partly sunny; then overcast again.
During the chase when Thunderbolt and Lightfoot are driving the Buick Riviera, another character puts a silencer on his gun, but the gunfire sound is not muffled.
When Red and Lightfoot are opening the wooden crates with crowbars, the lid on Red's crate opens completely with one pry and the Lightfoot even lifts the top on his crate up before he uses the crowbar.
When Thunderbolt and Lightfoot are being chased by Leary and Goody, they run their car off an embankment. It can clearly be seen that the passenger (Thunderbolt) is a dummy.
After Thunderbolt has sex with Gloria and she demands that he drive her home, the shots of Eastwood with the "bullet wound" on his right chest is revealed to be what it is, a plastic make-up application that is also peeling off.
There was a lot of money behind the blackboard but Lightfoot only had a small satchel of money with him at the end.
In the scene where Lightfoot drives a white van and chases a young woman on a motorcycle, streaks are visible on the right side of the camera lens in a couple of shots.
During interior shots of Lightfoot driving the white Trans Am into the wheat field, the camera can be seen attached to the hood.
As Thunderbolt and Lightfoot are being chased by Red and Eddie, Lightfoot careens the stolen Buick Riviera off the highway and down a steep embankment. Clint Eastwood's character (Thunderbolt, in the passenger seat) has obviously been replaced with a dummy. In addition, in some of the shots, a large camera assembly mounted behind the back seat of the Riviera is visible.
The car belonging to the crazy guy with rabbits in his trunk and a raccoon in a cage crashes and overturns. The damage is significant - a rear wheel is torn off and spins away. In a shot later, the pair are driving away in it. It's impossible that they could have repaired it, gotten it the right way up, and gotten the rear axle back together.
When Thunderbolt and Lightfoot are in the diner before being ambushed, Lightfoot orders a large breakfast, but when they leave, the jukebox is still playing the same song during the time it would have taken for Lightfoot's breakfast to be cooked and eaten.
After receiving a nasty kick to the head near the end of the film, Lightfoot is clearly seriously injured, as evidenced in the school house and in the white Cadillac, yet there are no bruises or blood, although his speech is slurred and he appears to have a concussion. Surely, Thunderbolt would have taken him to a hospital for medical treatment when he saw the distress he was in, except for the fact that, as criminals on the run from the law, they had to keep a low profile and a visit to any hospital would have been quite risky.
Though the gang is experienced, none of them wear gloves during the robbery. In fact, Lightfoot's finger prints would have been found on the bathroom doorknob, sink, and the faucet as he changed into his dress; and, after leaving the vault, Thunderbolt closed the vault door and touched the combination lock with his bare hands.