The warden has a giant wine cellar in his prison. During convict labor, the group of ten are assigned to clean this wine cellar. It houses a collection of 1,000 bottles of expensive wine. And many of these wines get put on the table during lavish parties hosted by the warden. A big one is coming up in one month. And his guests, well they are as bad as he is. They can't get enough of the warden telling stories about what sadistic puzzle he has invented for the prisoners this time.
So none of the ten prisoners have any qualms about what they are about to do: secretly poison nearly the entire supply of wine. They managed to get a special needle to inject the poison into the wine via the corks — the whole thing is untraceable. There are guards watching them, so they have to be careful. During brief unsupervised moments is when they strike, injecting one bottle at a time.
But it does not go according to plan. They are caught red handed before even the second attempt. And shortly they find themselves in a room, being viciously questioned by none other than the warden himself.
Eventually one of the prisoners explains the situation.
“We have poisoned only one bottle in your collection. But we will never tell you which one. And this poison is so potent, it will kill you no matter how many times you dilute it. It won't kill you straight away though. For 3 weeks you will not notice a thing, and then suddenly you will drop dead.”
The warden is furious. Foaming at the mouth, screaming: “How dare you! Do you have any idea how much these wines are worth?! I am not throwing out a single bottle more than needed!”
He gets silent for a moment and thinks deeply. Suddenly his angry expression changes to an evil grimace.
“Yes, that's right. I can still serve the remaining 999 to my guests. Because I will find this one bottle that you poisoned. And I only need the 10 of you to do so,” he claims confidently.
He lowers his voice, as he tends to do. “You will test my wines for me. Some of you will die. But you have brought this upon yourselves.”
What tactic could the warden possibly employ to make good on his manic claims?