Continuity mistake: When Goat dies, after the last attempt at defibrillation is made and the others give up, you can see the supposedly "dead" Goat take a big breath just before Reaper says "He's gone". In addition, in this shot Goat's eyes are wide open when the camera is on him. When the shot goes from Reaper back to Goat, his eyes are now closed. (00:41:05)Twotall
Trivia: The B.F.G. is a weapon that dates back to the game "Doom" back in 1993. There, it was the 'ultimate' weapon which, when fired, cleared the screen of foes in a great sickly green blast, consuming enormous amounts of ammo. It has showed up in various later games by both ID Software and third parties. Up to this movie, the acronym was never explained directly - although Sarge's version, "Big f**king gun" was for a long time the community's accepted name (also used in the original Doom design document, but not the game itself), and is most likely a homage to that.
Trivia: At one point Sarge tells his men to kill the remaining civilians to prevent the infection from spreading, an order which they all refuse. According to the back story of the first Doom game the reason the main character was sent to Mars in the first place was because he refused an order to kill innocent civilians.
Trivia: The marines activate "Kill cams" on their weapons. Doom's precursor game by id, Wolfenstein 3D, had a feature called Kill Cam, which was an instant replay of sorts against certain boss characters.
Question: What exactly happened to Reaper's parents? I didn't get much from the flashback, and it's almost never mentioned.
Question: In the end of the movie, why did Reaper grab the BFG? I could see the stock of the gun sticking out from behind him. It had no more ammo left, so what's the point?
Question: The scientists of the genetic research lab were first attacked by the Hellknight monster, which was actually the human test subject. Since after the incident the research lab was quarantined and the first Hellknight could have gone nowhere, how is it that the Marine troops didn't encounter the first monster even once when they entered the genetic research lab?