I might be interesting (if it is within the aquarium's husbantry codes) to see if a gentle petting of the mantle is well received. I have seen this in both my male two spots and with one mercatoris (Cousteau also reported that the female diver they worked with in Seattle had a gentle touch that would coax the GPO's easily for phtographing). Why they found it positive, I can't say but the hummelinckies returned over and over for light petting (barely touching). With OhToo we are just beginning and he will hem and haw for quite awhile before coming up to my hand but then either stays for petting or "pets himself" by moving against my hand or fingers. Octane expected me to offer my hand (no food smell!) nightly for the same purpose.
I wonder if they have any kind of a natural relationship with some type of cleaner critter. Nancy has remarked that Ollie liked to be petted similarly as well. Others have also noted that they like to sit in water streams (like the output of a powerhead) and I keep thinking there is something common here. Nothing earth shattering but interesting.