Lewis seemed to struggle with the higher notes in his songs.
At first, it seemed like there was a problem with his microphone or the sound mix, with some lyrics not coming through the PA system.
But soon it became clear that whenever Lewis would have to hit a high note, like in singing the title phrase from "This Is It," he would quickly and subtly slide the mic up from his mouth to his right cheek, next to his nose.
The mic he was using, which appeared to be a Shure SM-58, is designed to pick up sound directly in front of it, so it would seem that Lewis knew he would hardly be heard when he moved the mic away from his mouth.
Or maybe he was just getting over a cold or something. But probably not. Sadly, it is the voice, the one truly human element, that often goes first for aging musicians.
I’m thinking also of Roger Daltrey who arguably once had the most powerful voices in rock and now continues to perform with the rump version of The Who (it’s just him and Pete Townshend now, the other two original members of the band having already died). Daltrey’s voice is shot. Most recently, I saw the The Who perform on VH-1’s Rock Honors program and it was sad. Poor guy.