Unfortunately, this segment was removed in syndication.

From snpp.com:

Frink:
Well, it should be obvious to even the most dim-witted individual who holds an advanced degree in hyperbolic topology, n'gee, that Homer Simpson has stumbled into...(the lights go off) the third dimension.
Lisa:
[turning the lights back on] Sorry.
Frink:
[drawing on a blackboard] Here is an ordinary square --
Wiggum:
Whoa, whoa -- slow down, egghead!
Frink:
-- but suppose we exte-end the square beyond the two dimensions of our universe (along the hypothetical Z axis, there).
Everyone:
[gasps]
Frink:
This forms a three-dimensional object known as a "cube", or a "Frinkahedron" in honor of its discoverer, n'hey, n'hey.