Just as our visual system strains to see the vase and the two faces at once, we struggle to conceive of a motion that has a dual motivation: to put and to fetch. A paper by Van de Cruys, Wagemans and ...

It’s an illusion that dates back to Roman magicians, but the “cups and balls” trick continues to awe: three overturned cups, three balls and a magician that seems to make the balls move through one ...