It takes powerful forces to crack the human skull and threaten its precious cargo, the brain. But death can come instantly when strong forces threaten the brain stem.
Doctors think that is probably what happened to Dale Earnhardt after he crashed his car into a concrete wall at 180 mph.
His car stopped on impact, his body was held in place by restraints, but his head whipped forward with catastrophic energy.
The brain stem -- the nerve-rich segment connecting the brain to the spinal cord -- controls every breath and every beat of the heart. In such accidents, the nerve fibers inside the brain stem can be stretched, crushed or snapped. Death can be instantaneous. There is no pain, and no moment of realization that death is imminent.