In "Ain't No Kiddie Ride": Dr. Doofenshmirtz's evil plan is to write his name in the Ozone layer so that when the sun shines through it, it would burn his name into the Earth. He illustrates this by showing two slides, one of his name in the sky, the other of it being burned on the ground. The problem is that both slides show his name being properly written, when in actuality, the name in the sky would have to be written backwards in order for the name on the ground to be read properly.