Stare at the dot in the centre. Your brain is about to put colour into a black and white photo! Stare at the centre of the screen, the pink dots will totally disappear! Stare at 1 yellow dot for a while and the other two will become invisible to your mortal eyes!
Here's another one. Look at the centre of this picture and move your head back and forth, the stars will appear to move. More here: http://www.ritsumei.ac.jp/~akitaoka/rotate-e.html
ouch, just watching that 23hz demonstration gives me a headache.... I think the fluids in my head are reacting.