I've just rewatched Roger Ebert Should Lay Off The Fatty Foods (the one with the planetarium in it) and spotted a scene where the guy who runs it who says "plane_arium" 'cos of his strange bone disease actually says "planetarium" about three times in a row, without dropping the t.
It's during the second school trip just after Mr Garrison "has to go wee-wee".
(Or has this been discussed before at great length?)
Tony