Lisa: I haven't seen you in school.
Colin: Just moved from Ireland. My dad's a musician.
Lisa: Is he...
Colin: He's not Bono.
Lisa: I just thought, because you're Irish and you care about...
Colin: He's NOT Bono.
When Homer drives to the lake to dump the pig crap silo, there are hundreds of 'No Dumping' signs along the way, but on the way back, all the signs are gone, including the ones Homer missed.
When Homer and Bart jump the gorge, the ambulance that crashed into the tree in "Bart the Daredevil" is still there, crashed in the tree.