A kidnapper tells a pirate that he will be killed at 12:00:30 on one weekday in the following week but that the killing will be a surprise to the pirate and the pirate will not know the day of his execution until a half-minute before his death.
The pirate believes he will not be executed.
He begins by logically concluding that the execution can't be on Friday, because if he’s alive Friday morning he will know the day of his execution. [...]