They ask questions that they know you wont be able to answer because no definitive answer is possible, and to draw you into the answer they want so that they can attack your answer.
I've come across this approach many times, where they ask a very specific question knowing (or at least being very sure) that you won't be able to provide something that doesn't exist, so they can have their big "a-ha!" moment.
One example is on a discussion at ATS, where the poster demanded we tell him who took a specific photograph in cislunar space.
The answer "It was one of 3 people" wasn't enough, nor was any of the time and date specific evidence that it was taken exactly where and when it was claimed to be taken. A similar approach from the same guy was "I demand to see photographs of people in the CSM in Apollo 12". The fact that TV and 16mm footage was available wasn't enough, he asked
because he knew he wouldn't get what he was asking for and thus get to do a little victory dance (a photo of a reflected camera lens was dismissed as being of some sort of robot).
It some point the phrase "So you admit..." will enter the fray, because as we all know, information that they believe supports their argument is never given, it is always "admitted".
I summarise the approach as follows:
HB: "I demand evidence"
Sane person: "You mean like this evidence?"
HB: "No, not that evidence, other evidence that doesn't make me like an idiot."