It makes the monkey crazy. I'll walk through the living room without slowing, and as I pass by I'll say "you've got an extra space in the first line of that third paragraph. And down at the bottom you spelled his name Barrack, not Barack — he's not a military dorm."
"Arrgh!" says the monkey. "How do you DO that?"
I dunno. I come by it naturally, though — most of the people in my family can do this.