You know the rules. We all do. For better or for worse, they've become part of modern games design: barrels explode when you shoot them. Necks can be snapped with a single twist. Health packs give you 75 per cent of your health back. But could any of it actually happen? We collected the more common in-game rules and asked the experts what they thought.
Would a soldier really try and throw a grenade back at the enemy before it detonated?
Maybe, but it's unlikely. "The most basic human instinct is to run like hell and dive in a hole if you can," advises Lt Col Frank Keirsey, 24-year US Army veteran and advisor to the Call of Duty series. He's backed up by Commander Richard Marcinko, founder of Navy SEAL Team 6 and star of Rogue Warrior. "Throwing the grenade back is a reflexive reaction, not something you would train to do," he says.
If you did throw it, your chances aren't good. "If your opponent has not 'cooked off' the grenade, you have two to four seconds," says Kiersey. "So if the grenade landed close to your hand, and you were especially nimble, and there was no place to dive - yes, you might grab it and throw it. But I can't recall a recent account of a guy throwing a grenade back." Marcinko isn't sold either: "Not all grenades are the same. How long is the fusing mechanism? What type of grenade is it? Fragmentation? Pressure? Smoke? Flashbang?"
Do zombies exist? If so, is zombism contagious?
Wow: "A qualified yes," says Dr Jude Kelly of the College of the Holy Cross, New England. "There is one disease in particular that the whole zombie thing might have been based on." African Sleeping Sickness, spread by tsetse flies, has a range of unnerving symptoms, including "a change in personality, slurred speech, irritability, and difficulty walking." Victims tend to sleep all day and have insomnia at night. Professor Sanjeev Krishna of St George's, University of London, supplied more details: "This is an infection that carries nightmarish qualities, reducing many of its victims to a zombie-like state before they go into a coma and die." But what about that classic Romero breaking-out-of-coffins thing? Do those zombies exist? No, they don't, our experts said.
When do we get lightsabers? How about the Covenant energy sword?
Not yet. "A blade can't be made of light alone, since beams of light don't repel one another," offers Dr Kelley, although he doesn't rule it out completely. "If you changed the focal point of a pulsed laser along a set distance, the laser would ionise the surrounding air at each point, producing small plasmas. Create enough of these in a line, and you have a blade. It wouldn't block another similar blade, but it could conceivably slice through objects." So duels are out, but you could hurt someone - probably yourself, warns Kelley. "It'd need a huge, non-portable power source, would make a lot of noise, be extremely bright and probably blind or burn anyone you pointed it at."
Verdict: Probably never
Can you gene-splice your way to superhuman abilities?
Possibly. It turns out that BioShock's Andrew Ryan was way, way ahead of his time. "Gene therapy is a relatively young field that has shown some promise for the treatment of hereditary diseases," says Dr Kelley. "The simple idea is to replace a faulty gene with a more functional one." However, frost powers are a long way down the list, says Dr Frederick Chen of the Department of Family Medicine at the University of Washington. "We have only recently mapped the human genome, so manipulating it is still a long way off. Superpowers will probably have to wait until after we fix congenital defects, chronic illnesses, and cancer."