Henry hummed along too, that was just one of the things that helped him focus. There was an odd resonance to his humming, not quite an echo, but something close, it wasn't something that most people noticed, at least not consciously. It had to do with the fact that he'd learned to speak Shadow before he'd learned to speak English.
"Oof I'm rusty on the left hand." He said once the song had finished again, shaking his head, "I actually did worse than before, how about you?"