Wooden balls roll up the slopes just as if they are pulled by a magnet. The video is not a computer graphic, but a real scene. The orientations of the slopes are perceived oppositely, and hence the descending motion is misinterpreted as ascending motion. This illusion is remarkable in that it is generated by a three-dimensional solid object and physical motion, instead of a two-dimensional picture. Koukichi Sugihara
Meiji Institute for Advanced Study of Mathematical Sciences, Japan.