What does "instant death" really mean?
Dear Straight Dope:
When news organizations report on tragic accidents, they sometimes say that the victims were "killed instantly." What exactly does this mean? My friend tells me that it implies beheading, but this causes me to wonder about two things: (1) aren't there other things that could happen besides beheading that could kill a person instantly and (2) even if one were beheaded, couldn't consciousness be maintained for a little while, perhaps 30 seconds?
I hope you had money riding on this, Greg, because you'd have won big.
Trying to determine what news organizations mean they say somebody was "killed instantly" is almost impossible, and pointless besides--reporters aren't trained clinicians. That said, your friend is, I'm afraid, wrong. There are other ways for somebody to be "killed instantly," as long as we define what "instantly" means.
The main problem is that the moment of death is not always precise. Some mechanisms of death cause a rapid loss of consciousness--so the person would feel no pain--but actual physiological death may take a few minutes. For example, your friend's suggestion of decapitation would cause a rapid loss of consciousness, but the heart may beat for a few seconds or more before blood loss causes arrest.
Perhaps the best definition to use is any event that causes an immediate and permanent cessation of vital function, allowing for the slower process of cellular death. In layman's term, a quick and massive incident. For example, having your chest blown away by mortar fire, decapitation, getting hit by a speeding bus, getting a piano dropped on your head, or any other severe crushing injury to the head and/or chest, would all qualify. Another doc told me that any injury causing massive blood loss in a short amount of time could probably be defined as causing instant death.
Still, one suspects there's an element of fiction in the term--that it's something doctors tell the family to make them feel better. Yes, your relative died, but he did so "instantly" and without feeling pain.
Also, I should probably note that by a somewhat more snide definition, all death is instantaneous. One second you're alive, the next you're dead. It's like the punch-line to the old paratroopers' joke--it's not the 10,000-foot fall you have to worry about, it's the sudden stop at the end.
As for your second question, Cecil has already answered it--twice in fact. See http://www.straightdope.com/classic s/a1_221a.html and http://www.straightdope.com/colum ns/980612.html. Short answer: decapitation is usually about as close to instant death as you can get--but sometimes, maybe, it ain't.