The tip of a #2 pencil filling in an answer bubble on a scantron sheet.

I suspect most people in the US have found themselves on the business end of a Scantron® sheet before — the green-inked test response form that so uncompromisingly demands #2 pencils. In fact, the mere sight of one probably evokes a visceral, fight-or-flight adrenaline response in many Homo sapiens, much as the sight of a Smilodon did back in its time. It may not surprise you, then, that the gizmo that grades these sheets makes the instructor painfully aware of the errors. Feed in the products of the first exam of a class, your class, and every single mistake produces an unpleasant noise as the little mechanical sadist marks it. Bzz zz   zz zz    zz zz zz! It can be quite a cringe-worthy experience.