In the progression that starts "On the one hand..." and continues "On the other hand..." mainstream English may add "on the third hand..." even though most people don't have three hands. Among hackers, it is just as likely to be "on the gripping hand". This metaphor supplied the title of Larry Niven and Jerry Pournelle's 1993 SF novel "The Gripping Hand" which involved a species of hostile aliens with three arms (the same species, in fact, referenced in juggling eggs ). As with TANSTAAFL and con , this usage is a naturalized import from SF fandom.
