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The first time-derivative of distance is speed, the second is acceleration,
and the third is technically called jerk. Because we all sit in the gravity
well of the earth, we are under a constant acceleration of 1G. But when that
acceleration is changed dramatically -- and in a short time -- a significant
jerk is placed on the body. Unfortunately, due to varying inertias and
mechanical constraints, not all parts of the body respond to the imposed jerk
equally. The result is that the body's internal organs are differentially
ruptured and torn from their moorings. Vascularization tears are among the
most common forms of trauma under high-intensity jerk, resulting in massive
internal bleeding.

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Wirt,
Thanks for the graphics :-))  Now I guess I'll go *walk* home.

Anyhow, I used to ride bike (hi Terry) and understand it all to
well.  You can come off a bike a 125+ mph and just get bent a
bit.  It's the jerk that becomes memorable.  Kinda like the jerk
I'm starting to feel at watching our HP 3000 carted off down the
hall.  No blood though.
jt