IIRC it was the bug that allows you to pass through ghosts.  I vaguely recall learning about it because of something the author wrote when this was released.  Apparently speedrunners and the like have memorized patterns that exploit this if you can play with perfect timing.<p>Explanation of the bug at <a href="http:&#x2F;&#x2F;www.gamasutra.com&#x2F;view&#x2F;feature&#x2F;3938&#x2F;the_pacman_dossier.php?print=1" rel="nofollow">http:&#x2F;&#x2F;www.gamasutra.com&#x2F;view&#x2F;feature&#x2F;3938&#x2F;the_pacman_dossie...</a>, in the section &quot;Just Passing Through&quot;.