Growin' Like A Weed

I have been baffled by a mystery of science lately....maybe some of you could enlighten me with a logical answer. How is it that my backyard grass continues to grow even though we haven't gotten a single drop of rain since the remnants of Hurricane Ike rolled through DFW weeks ago? I haven't even watered at all and it just keeps growing! HOW IS THAT??

Don't get me wrong - I enjoy doing yardwork and have fun mowing, trimming, edging, etc. I even love raking and shoveling snow (which won't really be necessary anymore, though), so it's not that I mind the yardwork.....but I'm just not understanding the science/logic of it......