This app by necessity uses a more stringent capture process. When it is first started it captures a static background image. It then compares this with future images to determine where the forgeround moving objects lie. So ensure you are out of the image when you start the app. However you can recapture the background image at any stage by pressing the space bar. Note that even small lighting changes such as the moving sun will gradually throw the background image out requiring a recapture.
Press the left mouse button to cycle between clone mode where particles grab the colour of the webcam image and attract mode where particles hold their colour and are attracted to background motion. Once in attract mode you can use the right mouse button to switch to repel mode where particles are repelled by foreground objects. When switching to repel mode try to move to one side so that the clone mask slips off you rather than tearing apart.
For added enjoyment make a clone of yourself and then proclaim "I'm not a clone!" in your best Arnold Schwarzenegger voice. Works for me.