Version 1: (Webcam required)-when movement is detected, a clone of goo will disappear. One may need to stand away from his/her device for the cleaning process to be more difficult and for his/her hand to be the wiping device, rather than his/her head. Version 2: When one's mouse pointer touches the clone, the clone will disappear.
The inspiration is from the book "Coding Projects in Scratch"(--it's amazing-check it out), but the setup is entirely original (by me)