Try this.
1. Stare at the red dot on the girl’s nose for 30 seconds
2. Turn your eyes towards the wall/roof or somewhere else on a plain surface
3. Keep blinking your eyes quickly!
4. What can you see?
yep weird ,the girls image comes up ,bit like the exposure of an ancient camera ,the same thing happens when you stare at a coloured object for the same duration ,then look away ,you will see the same shape ,but in the opposite colour in the spectrum ,must be the receptors in the brain playing tricks.
Try this.
1. Stare at the red dot on the girl’s nose for 30 seconds
2. Turn your eyes towards the wall/roof or somewhere else on a plain surface
3. Keep blinking your eyes quickly!
4. What can you see?