Glad I found this post, Lokalai, since I've caught two of my E's doing that recently and I was about to start a new post about it.
Mine seem to do it most frequently next to the water dishes - my bigger E (Miss Piggy) will touch her front claws to the outside of the pool where it's wet, then do the quick rubbing together of those claws as if she's trying to warm them or trying to start a fire!
Meanwhile, she sort of hunker down and then she'll freeze and be perfectly still for anywhere from 10-20 seconds.
And then she'll get up, walk a few steps & do the same thing again. <sigh>
(Being OCD myself, I was a little worried it was some sort of abnormal crab "ritual" but then I caught my little E doing the same thing, and was reassured to see it wasn't just unique to one crab. (After all, if *everyone* is crazy, then no one is crazy by comparison.))
Still wonder why they do that though. <shrug>
Cheers! Elsie