[ I've learned to play dumb with certain things, if one person knows that I know something, suddenly everyone knows and I constantly get asked the same questions regarding it, thus I deny knowing that specific thing, now put that over the course of 40 years in the context of a mentally ill man who has a lot of pain tied up in certain memories, the last thing he is going to want to do is answer the same questions about something like that over and over again, it's easier to deny knowing about it.
I can't find it on YouTube, but I once saw a video where a fan asks him how he got the percussive sound on Do It Again. At first he says he can't remember. But pressed on it, he relates exactly how it was done. (I assume-- unless he was just making it up.)