I've just got back from taking my dog for his morning walk up the hill behind my house. The ground was wet so I wore my rubber boots (Wellingtons to Brits). As anyone who wears these boots regularly (or remembers wearing them as a child) will know, as you walk up hill your socks slip off your feet. This doesn't always happen though, it depends what sort of socks you wear. Today my left sock came almost completely off but my right one stayed on. What caught my attention though was that on the way down my left sock climbed back up my foot and was completely in place by the time I got home. I don't remember that happening ever before.
 It's all to do with the relative frictional force between the different surfaces. The friction between the sock and the boot is greater than the sock and foot so the foot moves backwards relative to the sock, as shown in the animation.