Stare at the black dot and move your head fowards and backwards repeatedly.

Count the number of black dots!

How many legs does this elephant have?

Stare at the black dot and see the grey area become smaller.

Are the grey lines parallel or sloping?

Man playing sax or woman's face?

Skull or vain woman?

One face or two?

Rabbit or Duck?

Native American's Head or Eskimo?

Is that a page of the book or the cover?