Please don’t try this. But if you close your eyes and flick your eyelid - it hurts, it really hurts. But you will also see a spark. The pressure on the eye causes the receptors in your eye to see a bright light - but there was no light and you had your eyes closed.
Our eyes are deceiving. Hundreds of optical illusions demonstrate how our eyes can be deceived. When my son was a toddler, he was particularly fond of his toy elephant. I took him to the zoo enclosure at Whipsnade and he held his toy elephant up to those in the far distance. Suddenly three elephants paraded past us on their daily walk. My son was shocked and burst into tears. He received a swift lesson in depth perception that day. He was totally traumatised, but a lesson, nonetheless. But close one eye and your own depth perception will also falter. That is also why one-eyed pirates continuously crashed their ships.
