About a month ago he learned to sit.
And then the next day he started to do what we call the "crawl and lunge".
See the scooting of the knees below:
And then when the arms aren't cooridinated to move with the knees you lunge:
And like I said, it's been about a month and those arms are showing no sign of getting on board with a coordinated crawl, so I'm thinking the crawl and lunge is here to stay.