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• Brace yourself: The spiral you see doesn't exist. Instead it's a series of complete circles. Try tracing one with a pencil and you'll see. The key to this illusion: the slanted black and white segments that make each line look like twisted cords. Those segments cause the visual neurons in your brain to signal that the circles slant inward, creating a false spiral.
• Look for that lowest step and you just go round and round, getting nowhere. (Sounds like your job, huh?) When your eyes and brain take in those straight, two-dimensional lines that form the staircase, they turn them into three dimensions. But they can only do this for one part of the picture at a time-say, a corner where the stairs turn and descend-not for the whole image at a glance. So you keep seeing pieces that make sense, even though the staircase itself is impossible.

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