The choice to hold the piece through the night for such a long time further goads the audience.
Basically, she was blatantly setting up the audience for this reaction. Repeat the same experiment in the middle of the day for an hour without putting a gun and knife on the table and you'll see a very different result.
EDIT: really, it's a piece of art about how it's very easy to manipulate an audience
EDIT 2: another downvote for not liking the same piece of art as you. Please grow a pair of balls.