After getting quite well along with the detailed drawing posted last, I began to get a nagging notion that I had seen it somewhere before. But where?
There are many known examples among writers of inadvertent plagiarism. We are not talking about the cases of blatant lifting of whole pages of copy that have made the news recently, but actual unknowing, unintended use of someone else's idea. You saw it or read it, you then forgot about it, but then at some point it bubbled up into your consciousness again, whereupon you thought it was your own.
At any rate, I realized that if I had seen this idea somewhere before, because of the arcane nature of the subject it would have to have been in one of my books on animation technique. And sure enough, I found it:
It's a little drawing by Richard Williams from his book "The Animator's Survival Kit". Still, I think my version is a justifiable re-imagining of the idea of extra fingers on the animator's non-dominant hand.
But that's not all I turned up! I also recalled an unpublished gag cartoon I had done years ago, circa the year 2000, and though I haven't been able to find the original, here is a recreation: