The paramedics, who rush to Frank Horrigan because of a report that he had a heart attack, never leave the office after it's discovered that it was a joke, yet they disappear.
In the final elevator scene, Frank's earpiece disappears and reappears several times.
When Frank and Lilly are disrobing on their way to the bed, you see all of their gear fall to the ground piece by piece and then their clothing. Lilly turns out the lamp, wearing pants, then lies down wearing a slip.
The pay phone has the off-hook sound when Frank goes down to look for Leary after hearing the fire truck in the phone, but Leary and Frank should still be on a live line.
Unless the three minute call was timed out.
Unless the three minute call was timed out.
After Lily steps away from Frank as he's playing piano, she walks across the room, exits the bar, then crosses the lobby to elevators. All the while Frank's piano playing continues. Once it stops, he clears the same distance in less then three seconds.
Lilly's gown during the party scene would be inappropriate for a female Secret Service agent, as it would prevent her from performing her duties should there be an attempt on the President's life. In those situations female agents instead wear dress pants and more practical shoes. (With the gown, there is also the problem of where to hide the service weapon.)
The Secret Service is shown inspecting manhole covers along the Presidential motorcade route. After the inspection, they place "Secret Service" security tape as a seal. Manhole covers are welded in place in reality.
Booth's landlady says that the United States is the only country where citizens can visit the office of the head of state. This is not true - Casa Rosada, the presidential palace of Argentina, is open to the public every weekend.
It is obvious when Leary is loading the gun that the pistol rounds are centerfire (having a separate primer) and therefore are not .22s. Most likely .32 S&W Short or similar. Otherwise the assertion that the composite would have had to have been highly advanced not to shatter when the gun was fired is correct.
At one point when the president arrives, a gaggle of photographers and reporters rush forward. In reality, the press would be very tightly controlled, even for presidential candidates who aren't currently holding office.
When we see Leary's view through his binoculars, his view forms the figure eight, but if binoculars are correctly adjusted, they form a circular view. This is a common error in movies, and is often made deliberately in order to show the viewers that now we see the scene through binoculars.
At the airport as Air Force One is about to depart, the same small crowd of people has been duplicated seven times, via digital effects.
When Horrigan is hanging from the ledge, the cut in the pipe can be seen before it breaks off.
As Mitch Leary assembles his composite-based gun at the Presidential Dinner, it is obvious that the thumbscrew is a painted metallic piece that would have been caught in the metal detector as he entered the event.
If such a small piece was challenged every time, a lot of zippers and earrings would be caught.
If such a small piece was challenged every time, a lot of zippers and earrings would be caught.
As Mitch 'falls' from the elevator, light can be seen glinting on his support wires, which also cause his shirt to be plucked up.
When Horrigan is in the cab, he takes out his gun and pulls back the slide to possibly put a bullet in the chamber, the slide locks back meaning the magazine was empty
The light bulbs in the elevator blow out before Leary hits them
When Leary falls from the elevator and hits the glass ceiling, the reaction seems to be that this is the bad guy, but it could just as easily have been Frank, as far as the people below could tell at that point.
The bank-clerk calls her dog "Lori" (or, perhaps, "Laurie"), but a shot at the end of the scene reveals clearly that the dog is male.
When Horrigan jumps across a roof, the harness and carabiner holding him to the wall are clearly visible several times.
When Horrigan is grasping for the roof, Eastwood's safety belt is briefly visible.
When the police cars converge on the St. Francis hotel, one of the cops forgets to put his car in park and has to get back in to stop it from rolling.
When Frank is talking to Lily in the President's suite he says when he heard the first shot he looked at JFK and could tell that he was hit. The first shot was a miss, striking the curb and leaving a gouge. In actuality it was the second shot, and not the first, that hit JFK in his back (then going on to hit Connally). The third was the fatal head shot.
At the beginning of the film, when Agent Horrigan is in McCrawley (Leary)'s apartment, he says to the landlady: "The President gets approximately 1400 threats a year ma'am, we gotta check 'em all". The U.S. Secret Service has a strict policy of not discussing either the number or nature of threats made against a president. No agent would ever make this sort of remark to a civilian.
Because the information it could reveal might be abused in the manner shown in the film, an active duty Secret Service agent would not be allowed to give such a detailed interview to a publicly accessible news source.
When the agent is checking the pack of photos against guests arriving for the dinner, Mitch's photo is a single frame. He then looks at Mitch, doesn't recognize him, and shuffles the now two-frame photo to the bottom of the pack.