Twisted Cord Illusion
Here are four equally spaced vertical black lines. To see them, click the Stop button and drag your mouse across the applet from right-to-left until the white segments are even. The black lines now look normal and straight.

Use your mouse to adjust the white segments to an extreme angle. Click Run.

The steeper the angle of the white segments, the more the black lines look distorted and bent. For more twisted cord affects, see the Frazer Spiral Illusion.