He told a room full of students that a French curve (that extremely curvy shape used in technical drawing) has the remarkable property that the tangent of the lowest point is always horizontal.. and they all believed him.
Well it's true, isn't it? I think that point was that they were astounded that the curve had that feature because they didn't understand why it was always horizontal. They thought it was magic.
Uh the point seemed that they knew the theory (of differentiation, tangents, trig etc) but were absolutely helpless in practically applying it. Couldn't relate the theory they had learnt to what they knew of the world, at all. Didn't think 'But the lowest point of ANY curve is horizontal!'
