At the scene Smith and DQ meet again, when DQ drops the ice cream glasses and start to kiss Smith she has her finger nails painted with pink polish, however on the next kissing closeup she hasn't no more.
In the final scene at the café, a fat guy is sipping his
milkshake having more than half of his glass empty. When Smith, angered by a row of irritants, starts shooting, a bullet breaks a fat guy's glass, which is surprisingly full. Also the type of glass is changed: the full glass, which exploded was not knurled, but smooth from the outside. (It also makes you wonder what the trajectory of the bullet was and where it ended up.)
When Smith first faces the "Lone Man" in the toilet shootout scene, Lone Man checks his gun, enters, lets off 4 rounds and reloads clearly showing that his gun holds six bullets. Smith then attacks him and in the ensuing fight the revolver fires eight times... well guess that explains what happened to the first two missing bullets?
In the brothel hallway when Hertz walks backwards and talks about the fingerprint guns, you can see the indicator light on Smith's gun showing green (as in print detected) which becomes red in the close-up view when Smith takes the hand out of his pocket.
In the scene where Mr. Smith jumps off the bridge, he shoots a few holes in the top window of the car, but as you can see, in the scene where he actually jumps through the window, there are no bullet holes.
In the first scene where Smith is sitting on the bench he's holding an Anthora coffee cup. Cut to closeup of him drinking from the cup and the cup is now one of the Greek style coffee cup imitators of the iconic Anthora coffee cup. Cut back to him sitting on the bench and the cup is now an Anthora again.
Even if the bullets wedged between Smith's broken fingers had gone off that quickly when he put them next to the fire, which is highly unlikely, without a barrel to direct the energy they would have basically amounted to firecrackers.
When Smith is busy shooting the bad guys in the warehouse, the last two shots he attempts to fire are met with the sound of dry-firing - a hammer falling on an empty breech. It is then shown to the audience that the slide is locked back, which occurs when the weapon runs out of bullets. In this condition the hammer cannot move, and the gun would not make any sound whatsoever if the trigger was pulled.
When Smith and Hertz point firearms at each other, Smith tells Hertz his Desert Eagle pistol is a six shooter. However, a .357 mag DE holds 9 rounds, the .44 mag holds 8 rounds and the .50 AE hold seven rounds. This would not include an additional round that could be chambered in addition to a fully loaded magazine.
In the bathroom scene between Smith and the Lone Man, Smith has dropped his SemiAuto in the toilet bowl and Disassembles it on the changing table to clean and dry the weapon for some reason. The gun would have functioned fine if he had buried it in sand, swam under the water or frozen and then thawed it. After having performed the cleaning and drying, there was no reason that the weapon wouldn't function, and drying the Firing Pin / Transfer Bar area under the hand dryer made no real sense other than Hollywood cool. Yeah, yeah, I know it was just one of many goofs related to firearms in the movie, but as an instructor, this one just stood out. I enjoyed the romp for what it was though, just FUN...
Hertz drives around with the corpse of the baby's mother the next morning, at least several hours after she was shot to death, yet there are no signs of rigor mortis (stiffness) or livor mortis (skin paleness).
In the car scene where Smith shoots out the windshield of his car and the van full of assassins the glass breaks into a few large pieces which easily fall out of his way. Car (and van) windshields are made out of two pieces of glass with a sheet of polymer or laminate between. This means that when broken (even if shot) the windshield will break into many small pieces, but these pieces will be held in position by the laminate. The glass used in the two vehicles for this scene are obviously not 'real' windshields. Furthermore, in a head-on collision of two vehicles traveling at the depicted speed, Smith should have been propelled all the way through the van's cabin, probably hitting his head against the back door.