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After a Friday night of drinking at Moe's Tavern, Homer walked home and took a shortcut through the forest. He saw what he thought was a green-glowing alien that said "Don't be afraid" in a gentle and pleasant voice. The encounter scared Homer so badly that he screamed and ran the rest of the way home. When Homer told everyone what he had seen, the report of his sighting triggered an FBI investigation (from Agents Fox Mulder and Dana Scully). When they found no evidence to corroborate Homer's story, they (and the entire town of Springfield) figured that Homer was crazy.
Homer was persistent, however, and returned to the scene the next Friday with Bart and a video camera. This time, the alien said "I bring you peace", and Homer tried to talk to it, but he stepped into his campfire and started screaming, which frightened the alien away. Fortunately, Bart recorded the whole encounter on video, including several seconds of footage showing the alien. The footage aired on Channel 6 News, and the following Friday, the townspeople turned out at the scene in force, hoping for a glimpse of the alien. When it appeared again, saying "I bring you love", they advanced on the alien and were about to beat it up when Lisa hollered at them to wait. Lisa shone a flashlight on the alien's face, revealing that it was actually Mr. Burns.
Smithers then appeared out of the woods and explained what was happening. Each Friday after work, he said, Burns underwent "a series of medical treatments designed to cheat death for another week". The program consisted of:
According to Smithers, the process left Mr. Burns twisted and disoriented. He had developed a habit of wandering into the woods dazed and confused following the treatments, which accounted for Homer's alien sightings. Bart asked, "What's with the glowing?" Burns, coming to his senses, said that he would answer that question himself: "A lifetime of working in a nuclear power plant has given me a healthy green glow." Burns then said that now that he was back to normal, instead of peace and love he would bring fear, famine and pestilence.
Burns was about to continue listing bad things he would bring when Dr. Nick cut him off by administering a booster shot. After receiving the shot, Burns reverted back to his "alien" self and led the assembled Springfieldians in a singing of "Good Morning Starshine".
 Behind the Laughter