Another camera technique that's pretty fun. Persistence of vision is the principle that makes the pictures in this entry "work," and the technique that produces these pictures is called light writing. It's like what you see in the Sprint commercials except that the Sprint guys make lots of the pictures and make play them as a stop motion movie.
Too lazy to read those articles? Ok, basically if you look at something, even for a little while, then look away, the signal that was sent to your brain is slow, so you see a sort of after image. That's persistence of vision. Need an example? Check out this Jesus illusion and check out the main site as well for some more optical illusions. They aren't all persistence of vision, but they're all pretty trippy. That's kind of what's going on in the camera when you set it on low aperture and a long shutter speed, like 30 seconds or even bulb.
If you take a picture with low aperture and long shutter speed at night, you'd get a picture that seems like it was taken at daytime, like the four second exposures from the Dupont hike and the time there was the power outage.
Now, get a flashlight, or some other bright source of light, and write or draw a picture while the shutter is open, and you get something like these pictures:
My first attempts at light writing-
I was holding the camera since I set it on bulb, so the background is blurry, and you can't see my hand, but in pictures that other people have made, they are in picture but are blurred, since they move around and the camera sensor is capturing all the light it "sees" while the shutter is open.