Thanks to the X-Men movies, everyone now knows about Wolverine and his limitless healing factor. One of the most valuable mutations in Marvel Comics history, his ability to heal from every kind of injury doesn't just make him invulnerable in a fight--it makes him immortal. The bad news is that the most unforgettable demonstration of Wolverine's healing factor ever seen happened in the movies… and it doesn't actually make any sense at all.
Obviously, the limits of believability need to be expanded when you're dealing with the X-Men, and a mutant who grows bones out of his arms like claws. To start with, Wolverine's healing could be real in a few decades. But even accepting the possibility of Wolverine surviving with a metal-coated skeleton, and accepting the miracle properties of Adamantium, there's no getting around the dumbest combination of these science fiction leaps. But in delivering the mistake, the film has made understanding how Wolverine's healing works needlessly confusing ever since. We're here to set at least this one screw-up right.
For the reasons mentioned above, every X-Men movie fan (no matter their feelings on the movie series as a whole) will remember the standoff with police involving Wolverine, Iceman, Rogue, and 'Pyro' in X2. Caught off-guard on Bobby's family's porch, Wolverine attempts to retract his claws to defuse the situation… and taking a bullet to the forehead from a trigger-happy cop. As Wolverine crumples to the ground, the audience knows he can't be dead. But it's how he goes about healing that causes all the trouble.
As the scene spins out of control thanks to 'Pyro,' Rogue watches (along with viewers) as Wolverine's body responds to the injury by slowly healing, and pushing the bullet out of his head in the process. Once completely removed, Wolverine's eyes fly open, mind alert once more. Effective on first viewing? Absolutely. But it quickly becomes one of the most nonsensical and misleading displays of Wolverine's healing factor when viewers ask themselves two questions. First of all, how did the bullet manage to enter Wolverine's head at all? And more importantly… why did he lose consciousness?
Before we even get to the type of healing on display, the scene makes little sense on the physics alone. While Wolverine literally is designed to kill, his skin is only figuratively thicker than a normal person's. And thanks to his Adamantium skull, the idea that the bullet could be 'pushed out' by Wolverine's healing is flawed… since it couldn't have gotten 'in' to anything to begin with. Even if you accept that the frantic cop effectively fired his gun at a head-sized metal ball and managed NOT to deflect it, the nature of Wolverine's metal adds a wrinkle to his healing factor in this scenario. Specifically related to his brain, and his metal skull's ability to absorb impact.
Knowing the differences between Adamantium and Vibranium, there's no question that Wolverine's skull is encased in the stronger of the two (the strongest metal on Earth, as a matter of fact). One might think that Vibranium would be the desired metal to prevent brain injuries, a high enough velocity round could impart too much energy for the Vibranium to absorb, and fail. But Adamantium? It would turn Wolverine's brain to mush before it ruptured (a variation of what occurred when taking two Adamantium bullets to the head in X-Men Origins: Wolverine). But a bullet is made to penetrate, and a 9mm like the one fired at Wolverine is nowhere near what would be needed to knock him out cold. Remember, he takes superhuman blows to the head that would kill a normal person on a regular basis, without issue.
Finally, we arrive at the real failure of the scene. The bullet shouldn't have impacted in his brain. It shouldn't have knocked him unconscious. And clearly, the skin of his forehead healing should have little to do with when he regains consciousness. But most important of all... Wolverine's healing doesn't actually work like it's shown. His healing factor will rebuild his body at an accelerated rate, but it isn't 'intelligent' enough to expel foreign material (and definitely not if a bullet was impacted directly onto his skull, like this one-in-a-million shot happens to be). In fact, Marvel Comics have shown Wolverine's healing factor can sometimes complicate the removal of bullets, by healing over them, rather than expelling them like an infection.
All these facts make it that much more tragic that this scene, like the later ones featuring Wolverine 'pushing out' bullets, are harder to forget than the comics they're based on. But at least now some fans have a clear sense of why Wolverine is made to be an unbreakable, durable, and ever-healing mutant soldier. And how many movie fans completely misunderstand his mutation thanks to flawed portrayals.