Killer Puzzle
For the last homework of the year, I gave my students a killer puzzle—literally.
Puzzle. A mysterious man kidnaps people, takes them to his cabin, and offers each victim two identical-looking pills. He claims that one pill is poisonous and the other is harmless. The victim chooses one pill, swallows it with water, and dies, while the killer consumes the other pill and survives. How does the killer manage to get the safe pill every time?
The official answer was that neither pill was poisoned. The poison was in the water.
Some students suggested that the poison becomes active only when mixed with water. I did not give full credit for this solution: saliva contains water, so the proposed chemistry is off.
Naturally, my students suggested other solutions. Here are two good ones, which are similar to each other:
- Both pills are poisonous, but the killer has taken an antidote.
- Both pills are poisonous, but the killer has somehow built up a resistance to the poison.
And here is an ingenious and highly specific answer from a student:
The killer kidnaps only people with deadly peanut allergies. He knows who they are because he is the town’s allergy tester, and both pills contain peanut butter.
ChatGPT offered a solution exploiting the wording: perhaps the victims die after swallowing the pill—but many decades later, of perfectly natural causes.
I feel there should be some more interesting solutions. Any takers?
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Inconceivable!
https://www.youtube.com/watch?v=rMz7JBRbmNo
11 August 2026, 3:27 pmIvan:
Are we sure the killer would take the poisonous pill, if the victim took the harmless one? Not at all. So, this could be a successful but unethical experiment:
Will suicidal people (carefully selected in advance) always take the kill-pill if I (the experimenter) gave them two correctly marked pills?
11 August 2026, 11:14 pmIzzy Grosof:
Another solution: the killer is consuming the pill via a different pathway than the victim – discount it under his tongue, or between his cheek and his gum. This leads to the pill being absorbed directly into his bloodstream, where it is safe. However, the victim swallows the pill, sending it to their stomach and intestines where it is processed by their liver. This subtly modifies the chemical in the pill, activating it and creating the poisonous substance, which kills the victim.
12 August 2026, 12:57 am