This post is not for erasing the data from the CD but erasing the CD and making it useless. With this method you erase the reflective metallic layer on the disc with electrical current. Data is saved on that metallic layer and by removing it you make the CD useless. All you need is high voltage and you will feel like Nikola Tesla. The reason you see it shrinking and disappearing is because CD recording medium is conductive and sparks follow the least resistance path. Sparks vaporize the medium from the outside because it is the nearest path and continues until it is gone completely.
How to erase a CD