It's psychological warfare.
Don't 'tell' him anything. Ask him a single question that you know he doesn't have a good answer for and don't provide the answer for him. Make him go away and research the question himself and obligate him to report his answer back to you. Make it a question that he can easily research using WT resources he has available in the KH library, WTLIB, or whatever it is they have available nowadays.
Don't let him morph the question into another subject that he would rather discuss. Give him a guilt trip for trying to fool you by avoiding answering your question and make him pay for his dishonesty by insisting that he answers the question that you actually asked.
They dance around awkward questions like politicians. Watch out for their tricks and don't let them get away with anything.