My husband and I were watching our son try to crawl on our bed. Forward crawling is no-where near sight, but there's a bit of reverse going on, but it feels partially unintentional. The concept of being up on his knees at the same time he's up on his hands is lost to him still. He covers a much larger distance when he rolls, although he also sometimes gets an arm stuck under him when doing this.
We watched him for a bit, encouraging him, laughing with him and playing with him. And it suddenly hit me:
Me: "He crawls like a defective hermit crab."