I like the one with Bart joining the Junior Campers... Homers throws a penut to catch in his mouth, it misses, and he says \'Something is very odd...\' then searches under the sofa for it, finds a $20 bill, then...
(Homer) \'A $20 bill? Aww, but I wanted a peanut\'
(His brain)\'$20 can buy many peanuts.\'
(Homer) \'Explain how!\'
(Brain)\'Money can be exchanged for goods and services\'
yada yada yada... I just love that scene.