And the answer is...

C

That's right folks, I got a nasty gash in my finger while opening a yogurt. Let me explain. This particular yogurt was a fruit-on-the-bottom type, having a plastic top as well as a foil lid underneath (in my experience the pre-stirred variety have only a foil lid, hence the distinction). In any case, with this brand of yogurt (store brand--Stater Brother's, we're coming after you...), the plastic top is very difficult to get off. The trick to a successful opening is to run your fingers under the rim of the plastic while prying upward. I've done it hundreds of times (with no ill effects, mind you), but on this unfortunate occasion, as I quickly ran my fingers under the plastic, a piece of the foil caught my middle finger (and sliced it).

Think paper cut. Think aluminum. That's right, think metal cut. The foil caught my fingertip at a slight angle, and, as it traveled through my flesh, it cut deeper and deeper. All the fingers on my left hand have thick callouses from playing the guitar, but I don't think they offered any sort of protection: the foil slashed through the callous (nearly lopping it off), and cut deeply into the skin underneath. After three days, it's finally starting to heal and is no longer an open wound. Yogurt eaters beware...