“what’s” –> “once”

For me, the causation of such mysterious typographical errors is not just a matter of sloth or clumsiness. Since they often come out in ways that are superficially intelligible but logically and grammatically impossible, I believe that intelligently studied, they might be able to tell us something significant about the way the brain and neuro-muscular system work.

I make such “transcription” errors frequently as well.