i gave mine a few transformers. one of them it disassembled at every joint and i found it scattered across the tank the next day. another one it ignored, and another one it very excitedly caught before it hit the bottom of the tank and pulled it apart. it showed some, though less interest when i put it back together and dropped it in again. another one is consistantly ignored. it reached out and took a hold of it, looked for a few seconds and then put it back in my hand.
all the moving parts and joints seemed to give it alot to play around with, just get one with alot of ball joints so you can pop everything back in place and let it start all over again. i have a few pictures of it with one if you type 'octopus prime' in deviant art.