Steve Higgins of Omni Brain swore his spinning dancer video is ambiguous. Swore it can be seen as spinning both clockwise and counterclockwise. I could only see it spinning clockwise at first. Then, after staring at it really hard, I can to understand why in theory it was ambiguous, but I couldn't see it that way. Now Andrew Sullivan has a still, which allows me to see the ambiguity. I think I caught it spinning counterclockwise once. But now it's spinning clockwise again, and I can't get it to change.