[navillusc]

I don't know about how fast a Yorkie can run, mine seem pretty quick, but I was aware of the bookcase incident a while back.

Sudden impact...the sudden stop is well documented in car crashes...the damage that can occur to internal organs even at fairly low speeds. As an example that I know for a fact happened...my DH, leaving the bathroom in no particular hurry, stubbed his foot on the doorway threshold and the healthy toenail on his little toe flew off...the threshhold was beside his foot...inches away. He didn't build up much speed in that 1/4 step, nor was he putting force into the action. He wasn't prepared to hit it, but to pass over it and although he was walking a normal walk for that millisecond, the speed, impact, sudden stop, etc. resulted in him losing his toenail immediately.

I have pondered that it isn't so much the speed as the impact...the sudden stop...that perhaps "speed" is merely a "modifier" capable of intensifying and/or increasing the amount of "damage" possible before the inertia resolves to normal for all tissues involved.