"Distorting lenses... imagine looking at a ruler in a curved mirror," he says. "You can see all the tick-marks even though it looks like it's a funny shape. Visual distortions don't change the underlying dimensions, and they don't change my perception of the underlying dimensions. But mirrors are interesting, actually, because they're almost like those optical illusions where it's two faces and you blink and it's a vase. I see the real relative position of reflected objects, but I can imagine the relative position they would have if the reflected light had been travelling in a straight line through a transparent pane. There's, um, a science museum back home that has a hallway lined with two not-quite-parallel mirrors, and I used to stand in it and make myself dizzy trying to see all the imaginary relative positions of all the reflected Ikes."