Figure 1: Scary's main window.
If you want a more ilustrative explanation, take a look on this video.
You can download the little program (zip compressed) from here:
Scary.zip tested in Windows and Windows Vista. The version for Windows XP is here: Scary.zip
If the links a above doesn't work, try these ones:
Scary.zip (Windows Vista, Windows 7, Windows 8)
Scary.zip (Windows XP)