ZAPHOD: Hey, this rock...

FORD: Marble...

ZAPHOD: Marble...

FORD: Ice-covered marble...

ZAPHOD: Right... it's as slippery as... as... What's the slipperiest
thing you can think of?

FORD: At the moment? This marble.

ZAPHOD: Right. This marble is as slippery as this marble.

- Zaphod and Ford trying to get a grip on things in Brontitall, Fit
  the Tenth.