(Up in the attic, Grampa shows Lisa a picture of Homer after he won his first-grade spelling bee.)
Lisa: Wow. Dad was a good speller?
Grampa: Oh, your dad used to be as smart as a monkey, then his mind started gettin' lazy and now he's as dumb as a chimp.
Grampa: Hey, I am too. And your brother's coming along nicely. Look at Bart's homework. Back when he was your age, he was as smart as a chimp.
(Grampa opens up a box labeled "Bart". On top of a stack of homework is a paper of Bart's from the second grade. It has a smiley face on it with the comment, "Great Work!")
Lisa: This is just two years ago!
Grampa: That's right. Then the Simpson genes kick in!
(Grampa leafs through the paper like an animator's flip book and the smiley faces on the corners of the papers gradually turn into frowns and eventually to a skull and crossbones.)