In a similar vein, I have a scar across my stomach from a university assignment that went wrong.
The task was a group engineering assignment, to build a catapult or similar launcher that could accurately place a projectile on a target disc in a variety of situations (over a high wall, under an overhanging branch, etc). We made ours out of a PVC launch tube with a pair of slits up each side and a bolt through as the launch device. The bolt was tensioned by a two pieces of surgical rubber attached to the top of the launch tube. We had calibrated the tube at various spots so that we could "dial up" a known amount of tension into the rubber straps to achieve known range, and and along with changes in tube angle the result was a simple, yet very predictable launcher that could land a spud softly on target every time. We were on track to get A+'s, and generally considered ourselves to be geniuses. Spying on the other teams revealed we were in the box seat for accuracy and power.
The final mark on the test (I kid you not - the lecturers were bigger kids than we were, if it were possible) was bonus points for the team who could achieve the greatest distance. Yup. So we were out testing the day prior. For those who've used surgical rubber before, you can put a MASSIVE amount of stretch into it, and get a massive amount of energy out of it. You know where this is going.
I was on the end of one of the straps, a mate (Anthony) was on the end of the other, and we were ratcheting up the power to see if we could get another 10m out of the launcher. Turns out, the strength of PVC tube, once you've cut two slits down the length of it, really isn't what it use to be. The tube fractured, and the launch bolt came loose. Ant copped a wack from the extended piece of rubber into his chest. I drew the short straw, and when the launch assembly broke, my rubber strap came away with the 10mm bolt still attached to the end of it, straight into my stomach. Ant was the first to realise what happened, when he worked out that if the steel wasn't on the end of his length of rubber, it must have been on mine. I was very lucky - could have easily been more along the lines of this poor bloke. Needless to say, with our launcher in pieces and half our team incapacitated, we failed the assignment.
As an aside, it's also a good example of why snatch straps and shackles are such dangerous things - same principle, just scaled up a bit with tons of force involved instead of "just" a couple of hundred kgs...
Anyway, that's my "Useless Story About Matt" for the day!
Thanks!
Matto
