Chopsticks Illusion

Each chopstick moves along a clockwise (CW) circular path.  their intersection also appears to move CW, although it really moves CW.  Conclusion: The CW motion of the tips propagates along the lines to the central intersection.

With the frame present, CW motion is seen correctly and eye movements (red trace) are accurate.  Without the frame, the intersection appears to move CCW and eyes can no longer track it properly.  (Blue spot was not present in original stimulus).