where are the 5 pounds hiding?

So, my weigh in revealed a loss of 5 pounds from the first time, which was kind of surprising considering I don't feel like I've made much progress. But even on my crummy scale, 5 pounds is a visible change. I guess that's why I wanted to space my rewards at 10 pounds, so I would know there was something significant, not just water weight or whatever. But don't look a gift horse in the mouth, right? I feel slightly, but not overly, encouraged. Hopefully with a bit more effort on my part I can see even better results.
I went to the gym on Thurs and did two different 20 minute programs on the treadmill with some pretty serious hills. It was way too cold outside, plus I need to pick up my gym attendance after throwing down all that money!