Doctor Who has finally explained how a Dalek gun exterminates. What would Doctor Who be without the Daleks? There is a sense of irony to that question, in that the BBC TV series was originally envisioned not as a science-fiction but as historical, taking advantage of the Doctor's time machine to explore critical moments in world history. All that changed when the Daleks were introduced — and they were a hit. "Dalekmania" swept the United Kingdom, and Doctor Who was changed forever.
Daleks may look like a race of malignant, malicious pepperpots, but the Daleks are lethal. They are driven by what the Second Doctor described as cultural xenophobia, a "dislike of the unlike" that causes them to seek to exterminate all other life forms in the universe. And they are ruthlessly efficient, wielding everything from Time Destructors to Death-Star-like guns on their starships. But their favorite weapon is their signature gun-stick, which sprays devastating energy beams that cause a body to flare with an unearthly light.
Robert Shearman's novelization of the classic Christopher Eccleston story "Dalek" finally explains how these guns work. The book reveals that the Daleks view death as a duty to be embraced, not as something to be avoided, and hence they had no interest in developing a way of killing that was painless. To do so would be dishonest. Instead, they focused on creating something that was as agonizing as possible.
"Dalek scientists devised guns that did not merely kill, they would exterminate. To kill suggests something respectful; one rids the body of life, but at the end of the process it may still be recognizable. To exterminate is something altogether different. To destroy from within so completely that no trace will be left, nothing that can be identifiable."
The Dalek gun is designed in Doctor Who to not affect the outer shell of a target, simply because a gooey mess is harder to clear up. But under the surface skin, everything has been scrambled — the heart, the bones, the blood, the kidneys, everything — and reduced to a thick mulch. This is why a shot from a Dalek weapon briefly acts like an x-ray on a target, making their innards visible for a brief instant. It's a horrific demonstration of the evil of the Daleks, who do not consider this a kindness exactly, but rather once again a demonstration of honesty. All dead things are reduced to the same state, as painfully as possible.
It is no wonder the Daleks are considered the most feared creatures in the universe in Doctor Who. Their entire philosophy, their understanding of right and wrong, is fundamentally twisted in the most horrific way. It's something even the Doctor has only occasionally realized, such as in the episode "Asylum of the Daleks" where he realized Daleks considered hatred beautiful, practically divine. But the Doctor should really remember this every time they see a living being cut down with a Dalek weapon.