In a game, two coins are tossed. If either of the coins comes up heads, you have won a prize. To claim the prize, you must point to one of your coins that is a head and say ‘look, that coin's a head, I've won'. You watch Fred play the game. He tosses the two coins, and he points to a coin and says ‘look, that coin's a head, I've won'. What is the probability that the other coin is a head?