Irene Lyon has just completed a sequel to her amazing Baby Liv video, which I posted about here. Part two looks at Liv's development into crawling. Watch it first for the cuteness, and then second (and third) to learn something about how humans develop their movement skills.
If you want to see another excellent video of a baby at play/work, click here for Charles-Edward.
And if you want to get to work/play yourself and recall what it was like to be in Liv's shoes, click here for some free Feldenkrais lessons.