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 & 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.