This psychedelic effect creates a spinning trail from your video clip. It adds a rotated version of the previous frame to the current frame. It works best on clips with a lot of motion. You can choose the center of rotation and the amount of rotation.
Settings
 
Angle
You can adjust this parameter to change how far the previous frame is rotated before it's added to the current frame.
X Offset and Y Offset
You can change the point around which the previous frame is rotated by varying these settings. They are expressed as a percentage of the frame's width and height, rather than in pixels, since your movie's size can vary. To rotate around the center, use 50% for both parameters. To rotate around the upper right corner, use 100% for the X Offset, and 0% for the Y Offset.