I've noticed, with both of the bimac's that I've kept, that if they are watching me from within their den, I can lure them out by using my hand to mimic the motions of an octopus. I do this from my side of the glass, not in the water. First I make my hand "jet propel" across the front of the tank, with my wrist leading, and my fingers trailing behind. My fingers start splayed apart, and then when I bring them quickly together, my bent wrist moves quickly forward about a foot. I repeat that a couple of times and my hand comes to rest on my knee, where it starts crawling, like an octopus, up my body, across my face, and then stops on top of my head. This always gets my bimac's attention, and he usually comes out to investigate.
Does anybody else do this?