OK, you garden detectives out there! My mystery plants are growing vigorously! Well, the first one is growing vigorously -- I'm afraid we'll never know for sure what the other one was because I forgot to water it and it died. Sorry. Did I mention I wasn't much of a gardener?
Anyway, the guesses on the remaining plant were: squash (crookneck?), melon (watermelon?) and cucumber. I ended up with about 20 plants, so I thinned them out this evening. The roots weren't deep and I didn't recognize the smell on my hands so I know for sure it's not zucchini. If you're new to this challenge and want to see what the seedlings looked like, click here. Anybody want to update their guess? Can you rule anything out?