There is a wonderful story about a group of military leaders who succeeded in building a super computer that was able to solve any problem large or small, strategic or tactical. These military leaders assembled in front of the new machine for a demonstration. The engineer conducting the demonstration instructed these officers to feed a difficult tactical problem into it. The military leaders proceeded to describe a hypothetical situation to the computer and then asked the pivotal question: attack or retreat? This enormous super computer hummed away for an hour and then printed out its one-word answer . . . YES.
The generals looked at each other, somewhat stupefied. Finally one of them submits a second request to the computer: YES WHAT? Instantly the computer responded: YES, SIR.
The Pharisees, like these generals, were accustomed to people saying "Yes, sir" to them. They were the religious authorities. Jesus' popularity threatened their authority, so they chose to threaten his with trick questions.