Character mistake: When Moss is arguing with the border guard at the Eagle Pass international bridge, he claims that he is a veteran of the "12th Infantry Battalion." There has never been such a thing as the 12th Infantry Battalion in either the Army or the Marines. Rather, they are based on a structure of 3-4 battalions per numbered regiment (i.e., 1st Battalion, 3rd Infantry Regiment/2nd Battalion, 5th Marine Regiment, etc). The film takes this seriously, as the guard, a veteran himself, buys Moss' story.
Suggested correction: He might have meant 12th Infantry Regiment. From Wikipedia: "Three 12th Infantry battalions deployed to South Vietnam with the 4th Division from August through October 1966."
If he said "battalion" but meant "regiment", then it's still a valid mistake for saying it wrong and being believed.
Regiments have not existed as functional units in the US Army since shortly after Korea; they are simply historic names associated with various battalions. Marine battalions are not numbered higher than 4 in any regiment, and in any case do not carry an explicit designation of "infantry."
Character mistake: In one scene, Ashley looks into Mr. Turner's yard with binoculars. She looks through the large glass circles. That would result in seeing everything smaller. If you want to see everything bigger, you are supposed to look through the small glass circles.
Character mistake: Chad actually steps on first base before the baseman has the ball. He was safe.
Character mistake: When Johnny Blaze plans on jumping the football field he says he is jumping field goal to field goal. The movie says multiple times he is jumping 300 feet. End zone to end zone is 300 feet. Field goal post to field goal post is 360 feet.
Character mistake: The endotracheal tube (breathing tube) was not secured to the patient. It is standard practice to secure this tube to the patient in order to keep it in place.
Character mistake: The definition of Satyagraha that Wilson, the butler at Harvard, gives is partially correct. Wilson defines it as "truth and fairness." A quick look at Wikipedia defines Satyagraha as "holding the truth." The definition from the online Merriam-Webster dictionary could be loosely described as "persistence of truth." (01:38:30)
Character mistake: The coroner examining Jennifer Toland's body reports that her fingers were cut off first, then the metacarpals (palm bones) were removed later. Given that when she is found her entire limb is missing up to her mid-forearm, how could he possibly tell not only that the missing part was not all removed at once, but which bits were cut off in which order?
Character mistake: When LT. Col. Robert Neville's wife fails the eye scan and he's ordering the soldiers to scan her again, the soldier that escorts them to the scan point, and later to the helicopter mistakenly uses Will Smith's real last name. You can faintly here him identifying LT. Col. Robert Neville to another soldier as LT. Col. Robert Smith.
Character mistake: As Lex is studying the recording of when Superman's body vanishes, he says "A 19 second black out at 3:47 AM." But the clock on the video shows it goes from 3:47:05 when the blackout starts, to 3:47:26. The blackout was 21 seconds, not 19. (00:45:55)
Character mistake: When Ms. Gruwell tells Gloria to read the first sentence on the board Gloria reads "Odysseus had no sense of direction." but on the board something different was written.
Suggested correction: The chalkboard had 5 sentences that were purposely written with wrong spelling and tenses. Gloria read the first sentence correctly as it appeared on the board "Odysseus had no "since" of direction."
Character mistake: When Mr. Brooks and Marshall hack into the police database and are looking at detective Tracy Atwood's financial records there is a screenshot of the computer screen showing some very terrible spelling.
Character mistake: John would not be able to contact the John Simon Guggenheim Foundation to obtain his sister's application history. The confidentiality of applicants is strictly guarded and would not be shared.
Character mistake: Roy says, "He thinks the wounds look self inflicted." But the doctor who said that was a female.
Character mistake: The oldest boy says "Here comes the calvary" instead of cavalry.
Character mistake: Nikolai is driving Anna home after the bike went kaputt in the rain, outside the restaurant. Anna towards the end tells him to "take the next right." Both Naomi Watts and Viggo Mortensen are looking left, and keep their eyes there. (00:28:25)