Who has never tryed to change the perspective of a cube drawn on a paper ? With a bit of concentration, you can imagine really well that the cube goes back in the screen or on the contrary sticks out from it.  In the same way in the picture on the right I get hold of the collier in such a way that its pointing towards me. Let's try and convince ourselves that it's otherwise and that it's point ing  towards the lens of the webcam...

Once you have carried out the above exercise, you can move on and play...
Take a collier like the one on the photo. Look at it with your arm streetched out in front of you and closing one eye. Choose preferably a light background – the sky or a well-lit white wall . If the collier points to the outside, concentrate until you convince yourself that it's pointing towards you. It's not always easy, but keep on trying!.. When you get there, don't let go! Keep this false image in your head. After a few seconds try and turn the colllier gently turning your wrist. If you lose the image, start again from scratch, otherwise you'll already be crying out with surprise as the collier seems to twist with your movements.

Buzzy explains: Why does the collier seem to be deformed ? Quite simply to make your visual sensations correspond with the interpretation your brain makes as the reality of the moment.. If the collier points towarsds you, by turning the the poignet to the right, the little circle should also move to the right; That's what you're expecting to see when your brain has succeeded in inversing the perspective. But of course, the inversiion is only an illusion, the collier doesn't point towards you and a ce titre, the liitle circle moves to the left. And so to stick together illusion and reality, the metal itself seems to be twisted!