Fiona: The Brain Spawn suppress intelligence by attacking the delta brain wave. Every animal and robot in the universe generates this wave, as do certain trees.
Nibbler: Fry, however, does not.
Fiona: Somehow he has cobbled together a random assortment of other brain waves into a working mind.
Leela: Like a prom dress made from carpet remnants.
Nibbler: Yes, like your prom dress.