Rick
I had a coworker many years ago that was an RC airplane enthusiast. He working on a rather large engine and prop, which he had affixed in a test vise on his bench.
With the engine running, which had to be loud, and the prop installed, he could see through the spinning prop, which apparently his eye didn't register as spinning because he could see through it, to a tool he needed. He tried to reach straight through that spinning prop and get the tool. It messed him up pretty bad for awhile.
I wonder if it was the same effect with a spinning cutterhead. Your eye just didn't interpret it as moving??
None the less. Hope you heal well, and once again at least have the Doc check it out. There's nothing on that cutter head that was meant to go in the human body.
"The first thing you need to know, will likely be the last thing you learn." (Unknown)