The Movie: Speaking of brains, let's talk about Khan's freaky trademark of crushing skulls with his bare hands! That dude is cold in more ways than one. In a riveting fight scene atop a spacecraft (we'll let that one slide), Khan gets a hold of Spock's head and for many tense seconds, increasing the pressure on the poor Vulcan's brain.
Real Life: Yeah, Spock would've suffered serious brain damage if that had happened. Let's consider Khan's first victim, Admiral Marcus. We see Marcus struggling in pain in Khan's crazy death grip, until his skull reaches a breaking point. But as anyone who has ever suffered a concussion can tell you, you don't need to damage the skull to damage the brain. Our heads have ingeniously evolved a nifty shock absorber, a coating of liquid called the cerebrospinal fluid. It is essentially the cushion part of the padded cell that is our head, and it protects the brain from minor blows. But it cannot protect the brain from the kind of force that Khan is applying. Such an incredible amount of pressure would cause a loss of consciousness long before the skull collapsed. Even if Khan had been stopped before the fatal crush, Spock's brain would have suffered major internal hemorrhaging. Logic your way out of that one, Commander.