I had known that some people could call a coin toss correctly far more than was likely by chance alone but thought that they somehow knew how to take advantage of the slight asymmetry between the heads and tails sides in coins. Maybe some do have that skill but others take advantage of an optical illusion as shown in this video.
It looks like it could be easy to learn so beware of betting on coin tosses unless you are the one doing the tossing and thus can be sure that there is no cheating.

