[SPOILER] Spider and Web: Uh, which puzzle?

Yesterday I took the time to play through Spider and Web, seeing as it won the IF Top 50 viewtopic.php?f=23&t=3272

A number of people in the competition thread talked about the game’s framing device, but many mentioned one particular puzzle, e.g. VictorGijsbers said it had “the most brilliant puzzle in interactive fiction.”

I beat the game, but I guess I missed the brilliance of that puzzle, because I have no idea which puzzle everybody’s talking about! Which puzzle is it?

It’s the one where you

break out of the interrogation chair.