Every Friday a member of staff at my workplace e-mails the 'Friday Puzzle'. I was prompted to post this revelation (;-)) when Dave's Scripting News linked to the Tech Interview site which is a good example of the type of puzzles that get circulated on a Friday:

this site is about challenging yourself to new puzzles and problems. do not be afraid that if a question you use appears here then it won't be worth asking anymore. first, people who come to this site to read the problems are the type of people you want to hire. they are the people who get excited about solving problems, and actively search out new problems to ask themselves.

Here's one of the Departmental Friday Puzzles that I was chuffed to be the first to answer:

A bad king has a cellar of 1000 bottles of delightful and very expensive wine. A neighbouring queen plots to kill the bad king and sends a servant to poison the wine. (Un)Fortunately the bad king's guards catch the servant after he has only poisoned one bottle. Alas, the guards don't know which bottle but know that the poison is so strong that even if diluted 1,000,000 times it would still kill the king. Furthermore, it takes one month to have an effect.

The bad king decides he will get some of the prisoners in his vast dungeons to drink the wine. Being a clever bad king he knows he needs to murder no more than 10 prisoners - believing he can fob off such a low death rate - and will still be able to drink the rest of the wine at his anniversary party in 5 weeks time.

Explain how....