About forty years ago I was told a tale by a military radar controller about “fast movers”. He was told to anticipate one and to disregard it. He was very much used to seeing high speed military aircraft pass across his radar screen and therefore wasn’t too surprised by the message.
However, in this case, he WAS surprised to see how fast the object in question passed across his screen. It appeared as just three “blips”, then was gone. He’d never seen anything moving anywhere near as fast as that before. But it was obviously known to the hierarchy.