Before going to the execution ground, the king said to the prophet, "Aren't you good at predicting?" Why can't you predict that you will be executed today? I'll give you a chance.

This is a logical paradox. The correct answer is: he predicted that he would be beheaded. If he is hanged, it means that his language is correct, but it is not true; If beheading, that is to say, the prophecy is wrong, but it is actually right because the king thinks the prophet's answer is correct, so according to his prior promise, he should let the prophet take poison and die, but this is just not in line with the answer of hanging the prophet, so he can't execute the prophet;