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This is the original drawing (pen/brush and ink on Bristol board, 7" x 20.5") by Ernie Bushmiller for the "Nancy" strip which was published in newspapers on March 12, 1971.
I'm not sure what to say about this one other than to suggest that you gaze upon its utter perfection. This is a typically minimalist late Bushmiller strip; it doesn't even have any word balloons! I love, too, the very subtle up-and-down placement of Sluggo within the frame, which gives this strip a nice rhythm, and the gag is, of course, executed flawlessly.
I have several other Bushmiller originals (see one from 26 years earlier here), but I'm withholding most of them until Pony Pal™ Mark's sure-to-be authoritative How to Read Nancy is published later this year.