I have a touch lamp at home. When I place a potato chip bag against it & touch the bag, the lamp changes. Why?

Ok, so it was a Cheetos� bag. Sue me. :P Anyhow, I just set the bag against the lamp, and the lamp changed. At first I thought the bag itself was causing it to change, but then, I realized, when I touched the bag while the bag was touching my lamp, the lamp changed lighting settings. I was so astonished, I decided to ask why here.