Every lab has particular occupational hazards. Chemists have to watch out for nasty acid splashes, biologists perhaps worry about inhaling exotic strains of bacteria. In a mechanical lab where you actually build things, you will occasionally need to work in a machine shop. And in a machine shop, no matter how careful you are, it's easy (for me at least) to eventually end up with various scrapes and bruises. It's the nature of the beast, and I keep band-aids in my desk to deal with small nicks (aluminum burrs are sharp little buggers).
I often use a piece of machinery called a waterjet - it cuts out 2-D shapes from almost any material.
You put your piece of material on the slats, and then a high-pressure jet of water and abrasive shoots down and cuts through the material.
On my waterjet, the slats are farther apart than shown in that picture. I had cut out a small little shape of aluminum, and I was cleaning off the abrasive from the finished part. Clumsy me, I then dropped the piece. Now if the piece falls to the bottom of the tank, you are never getting it back. It's just not possible.
So when I dropped the piece, silly me didn't even think about it - Quickly I reached between the slats, to catch the small piece as it fell between the slats toward the bottom of the tank. The good news is, I rescued my part.
The bad news, those slats are sharp. You see, the waterjet abrades away the slats under your material as well as your material - over time, the slats look like this:
Those little buggers are sharp. And they bit my arm.
Dang it. Had to go to medical and fill out a "workplace injury" form, which is a nightmare of paperwork. I felt like saying, I'm so sorry! I didn't mean to be clumsy, I'm just here because I need a slightly bigger band-aid than I have in my desk...
But they fixed me up nicely. And now I tell people I was knifed in a bar fight. I don't think they believe me... :)
So, lessons learned:
1) Don't be so clumsy.
2) Sacrifice your part, not your arm.
3) Be nice to the waterjet, or it will bite you.