When they wake up, the guys aren't happy about it, but they're otherwise immediately alert and aware -- Willis is even able to orchestrate a violent escape a minute later.

It also happens to Marty McFly at least once in every Back to the Future movie: He knocks himself unconscious and inevitably wakes up a while later in bed with his mother (or, in one case, a paternal grandmother who looks disturbingly like his mother).

But that's nothing compared to the repeated head trauma suffered by some TV characters -- you would see it happen repeatedly on Lost (usually with the butt of a gun) and Heroes (usually right before every commercial break). The character Giles from Buffy the Vampire Slayer was known for being a) super-smart and b) extremely prone to head injuries. These two things are not as compatible as you might think.

What would really happen:

We've all seen boxers and football players get knocked out for a few seconds and then jump up and continue playing the game (hell, it's happened to some of you reading this). But it's all about how long you are out. Experts say if you're ever out for more than five minutes, call a goddamned ambulance. There's a really, really good chance you have severe damage. A hit hard enough to keep you down that long means concussion or, worse, a traumatic brain injury or your brain may be goddamned bleeding on the inside.

And that's talking about being out a matter of minutes -- think about all of the movies you've seen where the character wakes up into some wacky misunderstanding hours later. In Pulp Fiction, the guy from the pawn shop has enough time to carry the characters to his basement one at a time, tie them to chairs and wait for his friend to arrive. By the time they wake up (not on their own -- they only wake up because their captor sprays water on them), Willis and Rhames can probably say goodbye to such helpful abilities as standing, walking, talking or maybe even waking up again.

And when you start talking about those TV show characters who are getting knocked out in every other episode, you're dealing with realism on the level of Elmer Fudd surviving getting flattened by a boulder. Concussions -- even mild ones -- have cumulative effects (as every football fan now knows). The more times you get knocked unconscious, the more severe your dizziness, disorientation and nausea will be each time. So, by the end of Back to the Future Part III, after being knocked out so many times in a period of like two weeks (or 125 years, depending on how you look at it), Marty McFly should be reduced to a drooling idiot incapable of walking by himself, let alone driving a DeLorean through time and space.

What we see in the movies:

If you don't have an explosion throwing the main character toward a camera, you don't have an action movie. You legally can't call it that unless your screenplay contains the words "runs in slow motion from the fireball."

Like in Mission: Impossible, when Ethan Hunt (Tom Cruise) is thrown by an exploding helicopter onto the back of a speeding train. Or in Mission: Impossible III, when the same guy's body is propelled by a freaking exploding missile, launching him sideways against a car ... only for him to get up, continue running and singlehandedly take down the airplane that shot him.

According to the physics of the Mission Impossible universe, jumping from an explosion involves surfing the shock wave. Tom Cruise is literally getting a little push from the inferno behind him, conveniently allowing him to reach a safe place more quickly. This also happens in the Die Hard franchise whenever John McClane has to leave a place in a hurry. By the fourth movie, he doesn't even flinch when a helicopter explodes right in front of him.

So it's kind of like getting pushed by a really strong wind. Your hair might get a little messed up, but otherwise you get to take a ride on physics.

What would really happen:

Notice how the same force was strong enough to tear apart the metal car or helicopter or airplane? It's not complicated; the explosion shock wave that can turn titanium into tissue paper will turn your body into a heaping bowl of human pudding. High explosives, like the kind you find in missiles, are hitting you with a force of around 1.5 million pounds ... per square inch. Basically, imagine a battleship landing on you. In the explosion business, they call it total body disruption.

And of course we're not even talking about the shrapnel flying toward your body, each chunk moving at the speed of a bullet. Or the ball of fire behind Bruce Willis that was burning jet fuel at 500 degrees Fahrenheit.

But maybe the hero was farther away from the blast than he looked, and maybe the explosion was just a gas tank instead of high explosives. In that case, you're only dealing with ruptured eardrums, burst lungs and bowel contusion/perforation. If you're not convinced that last one is a problem, go right ahead and do a search for that term in Google Images. Don't do it right after lunch, though.

What would really happen:

About 30 feet, or three stories, is all you get before you're dead. Falls from above that height are rarely survivable.

Now, we know what you're thinking: "Dude, this one can happen! People have totally fallen from airplanes and survived. I read about it on the Internet." And that's true, but those stories are famous for a reason. Surviving a fall is like winning the lottery. It could happen, but you're screwed if you count on it.

If you want to have any chance of surviving a great fall, you have to follow a pretty specific set of steps (arch your body, bend your knees, land on your feet, roll on impact and so on). And even then, the odds are still stacked against you, no matter what surface you fall onto. That sand or pile of garbage you're headed to might look ever so comfy and inviting, but when your body takes a run at it at 120 mph (the terminal velocity of a human body in free fall), you might as well be smacking a concrete wall. Even water hits you like stone at that speed.

Let's say you weigh 150 pounds and fall from a height of 30 feet. From that distance, you'll be traveling at close to 44 feet per second when you hit the ground. If you land on a hard surface such as concrete your body will be confronted with over 13,000 pounds of force. You know what that means.

So, if you get lucky and land on a softer surface, like a Dumpster with a few feet of soft fluffy trash to break your fall, you're still facing 1,500 pounds of force. And that's from a mere 30 feet up. In Transformers 2, our heroic group falls from a height of at least 50 feet. Not only do all of them survive, but they still look like this:

More recently, there's the scene in X-Men 2 where the military group breaks into the mansion and starts shooting darts at mutants of varying ages and sizes. Most of them are instantly knocked out -- except Wolverine, who's still standing after several doses because he's such a supernaturally big badass.

What would really happen:

Actually, Wolverine's reaction (that is, not being instantly knocked out by the darts and only becoming a little woozy) is one of the two most realistic outcomes from being hit with a sedative. The other one? Instant death.

A sedative works by suppressing your brain functions and artificially inducing a coma. That may sound pretty straightforward, but the amount of sedative needed to render you unconscious is actually excruciatingly precise. Teeter toward one direction, and the sedative will only annoy you. Teeter toward the other, and the same sedative can be fatal. It all depends on how big you are (so no, you wouldn't use the same darts on the Wolverine that you'd use on the children).

Further complicating the situation, the amount of sedative coursing through your veins has to be tightly controlled while you're unconscious, because "unconscious" can become "dead" more easily than you think. This is why anesthesiologists spend years in school and make lots of money.

Applying knockout gas is even more complicated, as the Russian authorities tragically found out during the 2002 Moscow theater hostage crisis. Perhaps influenced by their sexy Bond villain compatriot, the Russian special forces irresponsibly pumped a chemical agent into the building to subdue the terrorists ... and ended up killing over 100 hostages. Where's James Bond when you really need him?

And then we have the Saw series. Oh, boy, do we. Like in Saw V, when Mallick voluntarily puts his arm through a table saw to "win" the game. Or, you know, in every other Saw movie, since that's basically the whole plot of the entire series.

Mallick later passes out from the blood loss, but he eventually gets better and even reappears in Saw 3D.

What would really happen:

You die. Really quickly.

You see, your major limbs tend to contain major blood vessels. So when you lose one such limb, you have to deal with an inconvenient situation called "bleeding out." As the name suggests, that's when all your blood gushes out through the now-gaping blood vessels in your stump. And blood definitely won't do as much good outside your body as in it.

It is possible to survive losing a limb, as we've pointed out before. But to prevent bleeding out, you have to apply direct pressure to the wound or, in cases of severe bleeding, wrap a tourniquet tightly around the stump. Either way, the last thing you want to do is to keep moving around, since that will only increase flow of blood spurting from your body. The blood is carrying oxygen, and your brain needs oxygen to keep functioning -- that's why you'll likely lose consciousness in less than a minute.

In Saw 5, Mallick manages to stop the bleeding simply by disengaging his arm from the table saw. Luckily for him, his brachial artery apparently contains an emergency shutoff valve for when his arm accidentally springs a leak. Unluckily for him, he's still in one of the shittiest movies ever.

What we see in the movies:

Lava pits are popular in climactic fight scenes because they look cool as hell. See: Star Wars Episode III: Revenge of the Sith, Indiana Jones and the Temple of Doom and Lord of the Rings: Return of the King. Then you have the volcano movies (Volcano with Tommy Lee Jones and Dante's Peak with Pierce Brosnan). Let's also count the vats of molten metal in the steel mill at the end of Terminator 2.

No one ever has protective clothing, and everyone gets right up next to the white-hot material. In Revenge of the Sith, Obi-Wan and the newly anointed Darth Vader battle it out mere inches from a sea of flowing lava, never so much as breaking a sweat.

Except when Anakin falls into it, of course. Because the only way to be disfigured by lava is to actually touch it, right?

What would really happen:

If you've ever tried to rearrange burger patties over glowing red coals, you've no doubt realized that it's not just the coals that get hot: In a process known as convection, the air around an intense heat source tends to get super-heated, which is why you always end up giving your hairy arms a full Brazilian after you try to flip those patties.

And that's just from a pile of glowing lumps. Lava can reach upward of 2,000 degrees Fahrenheit. At that temperature, it's going to radiate a whole lotta heat. Exactly how much heat depends on how much of the intensely hot substance there is. Like, say, if you're watching a river of fresh lava oozing out from the innards of the Earth, you won't even be able to get within a few dozen feet before the heat is simply intolerable. Get any closer and you'll burst into flames.

In Revenge of the Sith, at the distance Obi-Wan and Vader are standing from the molten lava, it doesn't actually have to touch them to cause their bodies to combust. Though they were Jedi, so maybe the Force protects them from burns somehow ...

Check Dennis's musings on life and love here.

For more things Hollywood lied to us about, check out 5 Ridiculous Gun Myths Everyone Believes (Thanks to Movies) and 5 Things Hollywood Thinks Computers Can Do.