How are tricks played on your eyes?

Not sure what this has to do with football. The human mind and eye are not perfect recorders of events. The mind attempts to interpret visual stimuli in particular ways and can be fooled. MC Escher for example has some famous paintings where he uses the brain's bad habits to portray impossible scenes where stairways meet in impossible ways that seem logical. (http://www.globalgallery.com/enlarge/20783/) A man in a desert will see waves of heat rising off the desert and mistake the way they distort light for water just down the road, but of course, it isn't there. Do a google search on optical illusions and you will see no end of other examples.