I forgot to let Mr. Flywheel Cover be my friend
I had a "mini-bike" when I was 13. It was basically a small, extremely cheap motorcycle with a lawnmower engine. Because faster is always better, I made frequent modifications to the engine, one of which required removing the flywheel cover while the engine was running.

Around its circumference, the flywheel had dozens of sharp metal teeth which spun merrily around at several thousand RPM, just inches from my ankle. Ankle and flywheel were normally separated by the flywheel cover. But I thought it would be safe to ride it with the cover off for just one trip around the yard, if I was careful.

I wasn't quite careful enough. My right sock touched the flywheel's teeth, which immediately grabbed the sock and pulled it into the flywheel, taking my ankle along with it. The flywheel teeth then sliced efficiently into my flesh (this all happened in a fraction of a second) just as I approached my house.

My dad saw me leap off the mini-bike, blood dripping from the shredded remains of my sock; it was one of the few times I ever saw him look startled. He helped me hop into the house, where he performed basic first aid. He used several large bandages to hold the torn skin together, then told me to keep the leg elevated for a while.

As he was cleaning up the puddles of blood that I had trailed through the house, he said, "We won't mention this to your mother."
(unmutual, Mon 24 Dec 2007, 13:42, 1 reply)

At first glance
I mis-read "sock" as "sack" and almost didn't read the rest of the post as a result.
(Hagis, Mon 24 Dec 2007, 23:30, closed)