Once Gene Watson gets to the hotel and realizes who he's been sent to kill, he checks his watch. The watch in the closeup is a round watch. As we walks off and speaks to another person the watch on his arm becomes visible. It is a square faced watch.
At the end of the film, Johnny Depp's character falls into the lobby pool, then seconds later exits to the sidewalk but is not wet.
When Watson pulls the Governor's picture from the envelope, we can see through the photo, revealing that the face is visible to him. In the next shot, Watson starts pulling when only the hairline is visible.
When fighting with Watson on the stairway, Mr. Smith's hair is in his face on the closeup shot but is otherwise greased back.
The writing on the business card Watson attempts to hand the cab driver differs before and after the hand-off.
Watson says he's from Santa Maria, which is near Lompoc (California), pronouncing it
"lom-pock". If he actually lived there, he'd know it's pronounced "LOM-poke".
Watson's business card lists a Santa Maria (California) address. Santa Maria is in the 805 area code, but the phone number on his card has a 310 area code (Los Angeles).
Huey (the shoeshine man) tells Watson that he was wounded while serving in the Army Artillery Corps. First, the Artillery is a branch, not a corps. Second, Huey wears a Combat Infantryman's Badge on his vest. That award is given only to infantry troops.
When Depp approaches the van holding his daughter, he has a gun pointed at the head of the hostage accomplice. She fools him into thinking and he mistakenly believes that if he shoots her she can still fire the gun at his daughter, spewing about different caliber. If he did shoot her forehead, she would not be able to do anything else ever.
Huey's effort to faking deafness wouldn't never work. Deaf people cannot speak clearly and his tone would have to be way off and Mr. Smith would not be able to understand him.
The Colt revolver in the opening credits is a mirror image. The manufacturing roll-mark on the barrel is backward.
At Union Station, when the security guard attempts to stop the rollerbladers, film lights can be seen through a window on the right.
The taxi journey from Union Train Station in LA to the Bonaventure hotel cost Johnny Depp's character less than 4 dollars.
It's never explained why there is a plot to assassinate the Governor.
Huey actually blows his cover for pretending to be deaf in front of Mr. Smith, and gets away with it. When Smith tells Huey that he remembers a shoe shine to cost two bits, Huey responds with a head nod and a slight grunt.