The most successful toy has been a large Leggo block, used by Carol for several octos but we have seen it used by some of the aquarium/researchers (Carol has used it for years) articles as well. Only a few of Carol's octos have responded but when they did the outcome has been extremely interesting. Several learned to ride it, one even denned in it.
Ping Pong balls or floating containers were the first officially observed use of toys so surface floating objects that move in the current might be more the direction we should be taking.
Keys have been suggested often (likely because they are common and safe) but I don't recall ever reading that an octopus actually played with them. CaptFish had good luck with his bobber and lure but only for a short time (correct me CaptFish if I misunderstood the duration of play). As he aged, Kalypso became attached to the captured baster bulb he separated from a turkey baster and was allowed to keep it in his den.
In truth, I see the most interaction with feeding sticks at feeding time and often allow the octopus to keep it for a day (or until I see it released).
I have been experimanting with toys for Diablo, he seems very accepting to anything I introduce. Have tried pong-pong ball, rubber superball and plastic baby block all with ziptie attached to hold shrimp. He is very attracted to the shrimp attached but if left in the tank he does occasionally go back later and grab them floating at the surface. His favorite by far is my magfloat. I will caution that a very strong magfloat may pin an arm, this happened when mine snapped back onto the glass. I replaced it with a smaller, weaker one .
I have my thinking cap on searching for more interesting and unusual things to make toys out of. To be continued...
I am not sure what this seahorse's purpose was in it's past. There were 3 attached to a stand via metal rod through the center. It had a hole on top where we pushed in the bobber to keep it upright. Diablo will go back to it time after time and just hold onto it. Leaving it in till he tires of it.
There is also a hole through the center where I thought would be a perfect place for a zip tie in case I wanted to attach food. Hours after this photo was taken, I decided to remove the zip tie. My daughter offered to remove the seahorse. Here is what happeded.
It isn't from a store, husband found it at the recycling center. I cleaned it with vinegar rinsed well, just to be safe. It is a goofy looking odd thing but Diablo likes it. I have a bobber I am going to try and am going to keep working on the crab in a bottle.
During the night, Diablo pulled the bobber out of the top so I know it has been played with.
Interesting note and I don't know what, if anything, it means but in the photos with the seahorse, there is no dark ring around the eye, in the photos with the block, there is. Jennifer Mather mentions the "eye bar" (line in front of and after the pupil making the eye look straight) in Ceph's new book, Octopus: The Ocean's Intelligent Invertebrate as being a possible sign of being on guard and I have wondered about the darkening around the eye in brieareus (I don't recall them showing the line like the hummelincki but that may be lack of attention/remembering) being the same kind of thing. My guess it would be more you being attentive with food in the tank than the actual toy but it is something to watch and guess about.