In the depths of my refrigerator, left over from at least February or even times before that, sat a large (unopened) plastic-wrapped block of medium cheddar cheese. I hauled it out today (well, Monday, but that counts as "today" because I haven't yet slept) and took a look at it.
There were no funny spots. The thing looked just the same plastic-yellow color, and I determined that well, it's cheese. And unless cheese starts hosting alien life-forms or dessicating beyond repair, given that it's been sitting in well-supervised cooling...
So I tried it.
Evidently, well-packaged, well-preserved medium cheddar cheese turns into extra-sharp cheddar after it's passed its sell-by date by a good five months.
My inner cheese fiend has been having a field day, and secretly plotting to hoard packages of unopened cheese at the bottom of the refrigerator. If I still had roommates, at some point I would have naturally been questioned on the topic of why, and I would have had to have affected an innocent face and answered, "I'm sharpening them!" (The innocent face when I'm saying something perfectly outrageous is one of my special talents.)