Fillbert The Empty Space Cat

2022-W08: what is Fillbert

{Fillbert watches a CRT television.}Yellow: That news interview brings up a good question, Fillbert: What is Fillbert?Fillbert: I'm this spherical cat who fills empty space; I'm pretty cool. How about you?Yellow: I'm a formless shade of the colour yellow, but that's not what I meant. What is the webcomic Fillb-Fillbert: You're formless? I thought rectangle was your form!