Shape of F.D.C. Willard's pawprint
<a href="//commons.wikimedia.org/wiki/User:Dobromila" title="User:Dobromila">Dobromila</a>
CC BY-SA 3.0
own work, base of the image in Weber, Robert Lemmerman. More Random Walks in Science. CRC Press, 1982, 110. <a href="//commons.wikimedia.org/wiki/Special:BookSources/0854980407" title="Special:BookSources/0854980407">ISBN 0854980407</a>