Interestingly enough that particular turtle was blinded in a frostbite incident and was spending her days living in our aquarium. She absolutely loved when you would scrub her shell, so much so that she eventually equated the sound of bubbles from the divers to...HEY IT'S SHELL SCRUBBING TIME. The majority of the time we spent in the tanks was to scrub algae off the wall, and maybe we'd spend a few minutes at the end scrubbing her shell. She wanted none of that though, and would constantly swim into you while trying to clean the algae in an effort to get some scrubby time. If you ignored her long enough, well she made sure her presence was known and would take a nip at you hehe.