2014-10-04
Explanation
The Joke
A reporter confronts Superman about his X-ray vision, pointing out a fundamental problem with how it is usually depicted. The common perception is that X-ray vision works like a one-way signal where Superman sends out X-rays and receives the image back. But the reporter explains that the only way X-ray vision could actually work is if Superman has the ability to force human bodies to emit such intense radiation that it passes through thick barriers -- essentially irradiating everyone he looks at. The reporter asks: "You have the power to make people's bodies spontaneously emit huge bursts of energy. Is the power limitless? How do you do it? Why haven't you told anyone?"
The final panel shows a newspaper headline: "Another Reporter Goes Missing -- Superman Vows to Find Killer Himself."
The joke is that Superman silences the reporter to keep this terrifying implication of his powers secret, just as he presumably did with previous reporters who figured it out.
The Humor
The humor comes from applying real physics to a comic book superpower and arriving at a horrifying conclusion. Instead of being a benign ability to see through walls, X-ray vision would logically require Superman to bombard people with dangerous radiation. The comic takes the classic "Superman is actually terrifying if you think about it" premise and adds the sinister punchline that Superman actively eliminates anyone who figures this out -- while publicly "vowing to find the killer," a darkly ironic cover story. The newspaper format of the final panel is a perfect deadpan delivery.
References
The comic references the classic DC Comics character Superman and his well-known X-ray vision power. The physics discussion touches on how actual X-ray imaging works -- X-rays must pass through a body and be detected on the other side, meaning someone or something must be emitting the radiation.