As of Monday, Andrew is officially mobile! He started army crawling that morning. He is still trying to crawl on his hands and knees, but he still doesn't move much in that position and seems to go primarily sideways when he does. I've finally captured enough of his movement on video to post; these videos are from this evening while I was trying to read some magazines with Matt.
Once he gains even more confidence in his ability to move and figures out how to crawl on hands and knees he is going to be unstoppable.