Factual error: Neville shoots the propane tank in the kitchen, driving the darkseeker out into the hallway. Shooting a propane tank without an external source of ignition or a tracer would simply result in the tank's gas escaping and maybe the tank moving across the room. The Mythbusters needed an armor piercing rifle bullet to get through a tank and couldn't ignite it even with tracer rounds. Propane tanks are very thick walled. Bullet sparks are a movie myth. Bullets are either lead or lead in a copper jacket. Neither will spark when hitting metal.
Factual error: At the end of the movie when Neville is shooting at the darkseeker, he runs out of ammo and you hear repeated clicking as if the gun kept trying to shoot. He has an M4 and continuing to pull the trigger will not result in a click each time. You'd have to pull the charging handle each time you pulled the trigger to get a click.
Factual error: The scroll on the news reports the Patriots beat the Giants for the second time in the season. This could never occur unless the game was the Superbowl, as an AFC team never plays an NFC team twice in the regular season, and NFC teams and AFC teams do not play each other in the playoffs. The dates do not match up to the Superbowl, held in February.
Factual error: When the monsters breach Neville's house, in the scene where one of them is tearing up the ceiling while Anna and Ethan hide under the cabinet, Neville runs in, grabs what appears to be a Beretta M9/92f type handgun, and proceeds to shoot the monster several times. As he delivers the final "kill shot" the handgun is in double action (hammer is down). Unless Neville manually de-cocked the hammer, the weapon should be in single action with the hammer back, from the previous shots fired. (01:25:00)
Factual error: After three years, the gasoline/fuel supply used by Will Smith would have been degraded to the point of being completely unusable in a combustion engine or generator. Depending on the storage method, gas typically beings to break down after only several weeks. Even with a fuel stabilizer additive, after three years of storage the gas would quickly ruin the fuel injectors of any engine.
Factual error: When Robert Neville is driving golf balls off the deck of the ship, he sees a deer on the mainland. He and his dog go in pursuit. In a wide, distant shot, we see the deer fleeing full-tilt down a city street, with Robert Neville pursuing at the same speed as the deer, only about 10 yards behind the animal. Impossible. A panicked deer can run over twice as fast as the fastest human being.Charles Austin Miller