You enter the black and white death sequence when your health bar is reduced to zero. You have only a few seconds of life left before you collapse to the ground, but there's a sneaky way to evade your impending demise. You return to life if you manage to score four consecutive headshots on four different enemies during the death sequence. Your health bar is replenished by only a small margin when you return to life like this, so quickly move out of harm's way.