Optical illusions are caused by a trick on the brain which makes you think your seeing things that really not there., for example the spinning dancer, as you look at it one side of the brain thinks it’s spinning counter-clockwise and the other thinks it’s spinning the other way.
Another is duck or rabbit, this one is quite mind blowing due to the brain sees a bunny but not a duck due to the mind sees only a rabbit but if you turn look at it just enough you see a duck which the mind hides the duck deep into the image so your eyes do not see a duck and your brain starts to get creative and starts to see a duck.
Most people see the duck first and can flip between the two representations, but the question is: how easy is it for you to flip between them? Does it require real mental strain, or can you do it at will?
The last one confuse me is the three corners. The three corners messes with your brain they ask you if you see a triangle which a non real triangle to appear and thinks it is a triangle but it’s not real so it fools the person into thinking there is one, all it is just three corners, this effects the brain by putting the image in your mind which you will try to find one but as you search the mind soon thinks there is one in the three corners.