The Catbus appears on the road of the forest, when Mei, Satsuki and Totoro waiting for Tatsuo Kusakabe's bus to arrive. After the bus speeds a bit too fast and then backs up, it meows with it's glowing carlight eyes and smiles like the Cheshire cat (when he spots the girls), the girls make a random noise in surprise.
- The Catbus is most likely similar to the Cheshire Cat in Alice in Wonderland. (due to it's smile and it having stripes on the same area's).
- when a passenger wants to go on (mostly Totoro and the girls), it's sides droop down.... (not like a normal bus door that slides on the side.. but in the movie's real bus the door's are open with a lady standing there.. due to the it being the era of the 50's and it being in Japan they probably didn't have button's to open the doors like today).
- in the end credits you'll see a scene where Mei is drawing the catbus... but adding extra legs or skin windows....
- the only dialog you'll get is from the rodents above it, (most bus's don't have a voice intercom outside of the bus,... maybe in Japan,... but not sure since the bus in the movie didn't say anything so it could be they don't have an intercom or, didn't wanna add one, but the Catbus is the only one who has an outside intercom),... it could be the rodents talking or the catbus.
- here's more on this critter: http://en.wikipedia.org/wiki/Catbus