I've seen this kind of walk with other hummelincks but have not caught it on video. I am not sure Shelby is only using two arms but he definitely is walking upright without the assist of the live rock for part of the video. @mucktopus ?
Shelby had started to recognize the "play" corner and accept my fingers when I had to leave for a week to stay with my dad (valve replacement procedure went very well but he was not allowed to drive for a week). On my return, Shelby wanted nothing to do with me for weeks. Fortunately, something changed his mind in the last couple of days and he has again started to go to the corner and shown interest in exploring my fingers
Now that he is returning nightly to our "play corner" (he was totally avoiding the corner after I came home), Shelby is showing interest in being "petted". We have seen that several species seem encourage a light stroke between the eyes or on the front of the webbing. Not shown in the video, is an earlier contact where he placed himself under my finger and rubbed the front of his webbing against it. It is not clear if there is a "friendly" attachment or if their skin itches and a gentle rub acts as a scratching post (the later may be more the case as it seems to be more common in older animals). Why they seem to enjoy the interaction is not clear but establishing trust is required and takes a lot of patience and daily reinforcement.
Shelby is back to being antisocial but he did take an interest in the new clams I placed in his tank. These are larger than I like to get and very difficult for him to open. So far he has managed to open one after several days of trying but did not eat it. This is the second one that caught his interest and he spent a lot of time with it today but never opened it.
Shelby presents all kinds of color variations all the time. With other hummelinckies the color changing stops once they have become accustomed to the tank and they stay a rather boring brown. Not so with Shelby. I would like to get a shot of him in his all white with bright eye spot but this means he is mad and I usually don't have the camera out when he decides to be pissed off.