The Simpsons Episode 13.05 The Blunder Years

When Homer brings the family out for a nice dinner and a show, a hypnotist inadvertently conjures up repressed memories from Homer's past and causes him to scream uncontrollably. Realizing that he's been traumatized by some horrific event in his past, Marge gives him a special Yaqui Indian tea to sharpen his memory. Homer recounts when he was 12 and went on a hiking expedition with Lenny, Carl and Moe.

It turns out that while they were swimming in a quarry, Homer happened upon a corpse that fell out of a drainpipe. With the memory now out in the open, Homer is able to stop screaming, but the mystery of the corpse remains. The whole family goes to investigate and when they find the body again, they decide to follow the drainpipe up to its source. They arrive in Mr. Burns' office, where Mr. Burns tells them that the corpse is from Smithers' dad, Waylon Sr. Mr. Burns then shows them a movie about how Smithers' dad died, which was from the constant contact with radiation.