A dremel bit is a bit for a small tool that spins at extremely high RPM. Good for grinding, cutting, etc.
http://images.google.com/images?q=tb...20mototool.jpg
Now, when a small, hardened tool breaks for some reason, it still contains a lot of energy. When it breaks, it shatters, and pieces, with lots of rotational energy, fly outwards, kind of like a sharp explosion. Little bits of shrapnel. When you use a dremel, you often end up putting your face quite close to the work, so when a bit shatters, it sprays stuff all over your face, including you safety glasses. I'm sure they had lots of little cuts too, but in comparison to what could have been lost, its very minor.
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