Maybe not entirely a secret, but at least a confirmation of rumor.
There's a picture showing Sandro Carella by a wall of sketches.
Look closely, and you'll see that the sketches are of classic racing
cars. This seems to confirm that, indeed, Papyrus is working on
the classic racing simulation I've been saying for years would be
a load of fun.
Also, on the next page, there's a picture of someone, and on his
computer screen is an IndyCar which appears to be slightly airborne,
or riding up against a retaining wall. Whether this is a real image
or computer generated can't be determined, but if it's the latter,
then perhaps Papyrus is working on 3-D physics models for future
sims.
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http://www.racesimcentral.net/~keeper/toons.html - Contemporary WB cartoons info
http://www.racesimcentral.net/~keeper/midi.html - My own MIDI music and arrangements