@liberosist very killer find. I'd be curious to see if he could sing words backwards. Based on the cognitive loading experiments, if he was not playing an instrument, I'd be curious to see if his brain could adapt to that and still permit him to sing backwards.
I was wondering the same when he picked up the banjo. I guess that's much more difficult as one sings to the rhythm, and the rhythm can't be backwards. Unless he learns how to play backwards too...