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 became one of the naturalized imports from SF fandom frequently
observed among hackers.