It appears that I now have a partially mobile baby on my hands; yesterday morning I put Sammy down on the floor with some toys and went into the kitchen to wash his bottles for the day. You can imagine how surprised I was to find him on the other side of the room when I checked on him a few minutes later.
I don't exactly know how to describe how he's moving himself; it's weird combination of raising his upper body off of the floor while attempting to get into the kneeling position, but failing, and then sliding backwards as a result. Here's a little video of him doing his thing or rather trying to at least:
I think if he keeps this up, he might be crawling sooner rather than later; I hope Sandy's ready for this!