Throw your Pencil a Curve

Try this:

• Grip the end of a pencil, hold it vertically, close to your face, and wiggle it.

How come the shadows are curved but the pencil's straight?

Motion made the pencil's shadow stretch out to a diagonal, just like before. But when you wiggle your pencil, the end moves farther and faster than the part you hold. So the fast-moving end casts shadows that are strongly distorted into a diagonal; the slow-moving part you hold, doesn't.

The result:

A shadow that appears more and more diagonal the further along the pencil you look.

In other words, a curve.