Whimsy: January 2012 Archives
It was a running gag in Walt Kelly's comic strip Pogo. Friday the 13th was a baleful day, particularly when it fell on a Friday:
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Here's the Friday the 13th sequence from the summer of 1965, via Whirled of Kelly, a blog devoted to the art of Walt Kelly. Click on the strip to go to the corresponding entry on that blog.
And from March 1970, via Active Rain: