In an earlier version, Iris's timekeeper discovers a weapon on Travis, disarms him, then returns it to him as he's leaving. The scene was edited out, but the gun is still in the timekeeper's hand when he looks at his watch.
When Travis sits down with Wizard and Doughboy at the Belmore, he orders a cup of coffee. Seconds later, when he puts the Alka-Seltzer tablets into his water glass, a hamburger is on his plate.
Travis has a shorter haircut only for the "Secret Service guy" scene.
Travis burns the flowers in the sink. Soon after, when he puts money in an envelope, the flowers are on the floor behind him.
When Travis and Iris are having breakfast at the coffee shop, the parked cars seen through the window behind Travis, change between every shot.
When Travis seals the envelope with money and a letter to Iris and puts it down on the desk, the postage stamp is already canceled as if it went through the post office.
On a newspaper clipping at the end about Iris and her family, Pittsburgh is misspelled as "Pittsburg," without the "h."
Travis, a Marine Corps veteran who states he was discharged in 1973, wears embroidered Navy parachute wings on oval cloth patches on the two military jackets (one of which is an anachronistic WWII-era "tanker" jacket) he wears in the film, which would indicate he was in Marine Force Reconnaissance (Recon). The wings patches are incorrectly placed on the right breasts of the jackets, as U.S. military qualification insignia are always worn on the left breast.
The street performer with the snare drum refers to "...40 years of Chic Webb". Webb only lived to 34, and was only in the business for 13 years.
The black market gun dealer says the semi-automatic he sells Travis holds rounds in a 'clip'. Pistols don't hold rounds in a clip, they hold them in a magazine.
Iris's sunglasses change from green to blue when they're having breakfast. This is a character quirk; she changes her glasses periodically, as the person Iris was modeled on did this.
When Travis is buying the guns, he holds the gun in his right hand, but he sights down the weapon with his left eye. Although this is uncommon there are a number of right handed shooters who are "Left-eye dominant". This can be uncomfortable when shooting high powered handguns as the hammer tends to kiss the shooters forehead.
When Travis oils his sliding gun contraption, he does not take the cap of the oil bottle. The 3-in-1 oil does not have a removable cap. The red thing on the tip is a closure. You pull on it to open and press to close. It does not remove completely.
During the politician's speech on the street, a number of extras are obviously looking straight at the camera, including one man who waves to it.
While Travis is checking the .44 Magnum revolver offered by the gun dealer, the cylinder emits a clicking sound while he spins it. In fact, the cylinder of a double action revolver such as this one does not click when it is rotated.
When Travis is negotiating with Matthew for Iris' services, an off-camera voice says "But no rough stuff." just before Matthew says it.
In the shot from Travis' point of view, when he passes the Palantine office and sees that Betsy is not at her desk, the cameraman and dolly grip are clearly reflected in the window.
Reflected in a storefront window, in a drive-by shot of the campaign headquarters.
When Betsy gets into Travis's cab in the final sequence, she never tells him where to take her. He just starts driving.
The first time Travis has coffee with Betsy, Travis' voice-over states that he had black coffee. A few moments later, milky coffee is visible.
Travis says July when reading out loud his message to his parents on the anniversary card. When the card is shown on screen, it appears to read June.
According to the exterior shot, and the Then-and-Now Special Feature on the 2-disc DVD, Iris lived at 226 East 13th Street. Travis writes "240 East 13th Street" on the envelope containing the letter and $500.
The black-market gun dealer misidentifies the .380 Astra Constable in his case as a Walther PPK. The guns are very similar, so it could be an easy mistake or a deliberate lie. He tells Travis the Walther PPK .380 replaced the P-38 as the standard German military sidearm in WW2, which is false. The P-38, a full-size pistol, replaced the P-08 (Luger) as the standard military sidearm. The PPK was a compact pistol for use by police (PP stood for Polizeipistole) and personal protection, not as a combat sidearm.
When Iris is talking to Travis in the diner towards the end of the film she states that Sport is a Libra just like her which is why they get along so well. Then adds that Cancers make the best lovers; on this assumption one believes that she knows a lot about star signs. However, she then says that Travis must be a Scorpion; the star sign that she is referring to is Scorpio not Scorpion.