Filler art

From The Heretic Knowledge Vault

Drawings by Poe that are inserted into the thrice-weekly sequence of strips when real-life circumstances don't allow him to complete a strip to his satisfaction in time for publication. (Think of them as Fan service.) Many feature characters from the strip; others feature Poe himself and/or Impy in various predicaments; others just come from Somewhere Out There.

An example of filler art involving catgirls appears here. It isn't clear whether filler art featuring actual ES characters should be considered canon for purposes of character development, etc.