Hayao Miyazaki is often called Japan's Walt Disney, but I hate to think of him as a racist and vindictive bastard who would name names during a government witch hunt.
I was always freaked out by the whole door thing... It's not a limb he can move, there's no apparent "door-lid" he could open and close... it just ... makes a gooey transformation.
As a plus, you never have to worry about idiots spilling their food and drinks or playing loud Top 40 crap rock or rap over their MP3 player/cell phones on the Catbus.
Catbus will not have any of that going on inside him on his route.
proper use of the "also his balls are huge" tag. That was one of the first things my friends mentioned when I first saw this movie. "Oh, it's great. There's a Catbus and it has balls!"