Continuity: When fighting with Watson on the stairway, Mr. Smith's hair is in his face on the closeup shot but is otherwise greased back.
Factual errors: 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".
Continuity: The writing on the business card Watson attempts to hand the cab driver differs before and after the hand-off.
Continuity: 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.
Factual errors: 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).
Crew or equipment visible: At Union Station, when the security guard attempts to stop the rollerbladers, film lights can be seen through a window on the right.
Continuity: When Watson's in the hotel, he takes a look to the clock and it changes from 1:26 to 1:27, then he takes a look again, and this change happens again.
Errors made by characters (possibly deliberate errors by the filmmakers): 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.
Errors in geography: The taxi journey from Union Train Station in LA to the Bonaventure hotel cost Johnny Depp's character less than 4 dollars.
Continuity: 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.
Factual errors: 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.