Hu and Edwina's Chevy alternates between a ;72 Impala 4-door post sedan and a 1974 4-door hardtop quite blatantly throughout the film.
When Ed picks up Hi in the back of the grocery store the right outside taillight is out, but after Hi grabs the bag of Huggies the light is working.
During the taking of the first "family photo" on the couch, H.I. frames up the shot with a Canon camera, as it snaps the picture it is a Nikon.
When Glen comes back with a neck-brace the curtain on the window of the trailer door changes to a Venetian blind, and then when H.I. goes back inside the louvers change from closed to open.
When Hi goes into the Short Stop the parking lot is wet with puddles. The police car comes over the wet bridge and stops in the dry parking lot. Then the roads are wet again.
In the Northern hemisphere, the sun and moon rise from the horizon up and to the right, but it was shown rising up and to the left (which would only happen in the Southern hemisphere or when filmed in reverse).
The grocery store manager is clearly seen putting two shells in a double-barrel shotgun, but then fires at H.I. several times in rapid succession. (Intentionally done by filmmakers to illustrate how H.I. can never catch a break.)
During the wild chase scene in the "Double Coupons" store, the police officer fires nine shots from a chrome-plated six-shot revolver. This is probably intentional as with the clerk's "magic" shotgun.
The face of John Goodman's stuntman can be seen when H.I. throws Gale onto the floor at the beginning of their fight.
When Hi comes out of the Arizona mansion without one of the kids, and Ed demands that he go back and not come back without one, at one point during her rant, she rolls up the car window all the way, but you can hear her talking at the same volume.
The "Thrush Muffler" trademark tattoo on H.I.'s arm switches sides when
he is chasing the babies around on the floor in the initial kidnapping scene. (flipped shot?)
The "Deep Southern" accent of the main characters is not typical of Arizona.
When Snoats is pulling himself out of the mud, you can tell he's being pushed from below. He is still rising when his arms are in the air and not pushing against the ground.
In the Full Frame or Pan & Scan version, when H.I. is in the Arizona house kidnapping the baby, one of them "jumps" out of the crib and onto H.I. In the shot where the baby lands on him, a person's hands can clearly be seen at the top of the frame holding the child.
Dolly track visible on ground as H.I. and Glen discuss wife swapping.
In shot in which the blue dye pack explodes, ear plugs are visible in both Goodman and Forsythe's ears. This is likely due to the volume of the explosion.
Shadow of camera operator and vehicle while Leonard Smalls is cruising down the highway.
The police take Nathan Arizona's fingerprints in order to separate his from those that the kidnapper may have left. Since Hi didn't use any gloves when he entered the quintuplets' room and since he has a criminal record (with his fingerprints on file), shouldn't the police learn his identity immediately through the fingerprints he left on the window sill and elsewhere?
"It ain't armed robbery if the gun ain't loaded" is false. Even a toy gun that appears to be real suffices in Arizona to support a charge of armed robbery.
When the FBI is questioning Nathan Arizona as to what the kidnapped child was wearing, Arizona says the child was wearing jammies even though all five babies are shown wearing just diapers.
When H.I.'s form is red-stamped "PAROLED", the word "Searched" is misspelled as "SERACHED".
Comma placement in the newspaper. The sub-headline in H.I.'s stolen newspaper: "More than we can handle", laughs Dad. No editor at a paper, no matter how small, would miss the incorrect comma placement, which should be inside the quotes. It should say: "More than we can handle," laughs Dad.