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''When we first tracked the r-pentomino (you'll hear about that soon) some guy suddenly said 'Come over here, there's a piece that's walking!' We came over and found Fig. 9''

Elwyn R. Berlekamp, John H. Conway, and Richard K. Guy. Winning Ways for Your Mathematical Plays. Volume 4, Second edition. p. 931

According to the lore, the 'guy' in the passage above was Richard Guy. [interpretation of 'Fig. 9' reproduced in pennies above]