Edit to add relevant lyric; 'If infinite monkeys type every day, they may accidentally write Hamlet the play. But they'll probably just shit on it and throw it away. In the Infinite Monkey Cage (those naughty monkeys)!' -Eric Idle
It was closing the unknowns in the narrative. The joke was supposed to offend him. How would we know that it actually offended him if he didn't say that (or react in some way)?