How does a Pringle Pinhole Camera work?

imagine you're in a room with all the Windows blacked out, you cut a small hole in the black out material allowing a small amount of light in, looking at the wall the light is projected on, you will see an upside down image of what is happening outside, this is how the pringle camera works, i did this on my taster day at college, hope it helps :) if you have the patience there is a video on bbc about it, but i'm not sure what it is called.