> Sorry, perhaps I wasn't specific about my "idea".  (-:  I meant
> I thought I could maybe do one where you have to look at it and
> shake your head NO! over and over to read it

Well, it is kind of do-able, but could be quite uncomfortable. You'll
have seen clock displays that flicker when you turn your head, and
indicator LEDs that maybe use 50/60Hz AC and which also appear
to make a dotted line (persistence of vision again), so the effect is
there. However, with the LEDs moving, everyone present will be
seeing the same thing, head moving or not

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