"You may take back the card you just played," said the Headmistress, and a gasp went round the table: mercy, from the Headmistress, of all people.
"Once," the Headmistress added.
The table had been waiting an hour for the Headmistress to be wrong about something, and had been disappointed. The player, who had just made the worst move of their life, picked the card up before anybody could change their mind. "Do try to think first," said the voice, cool as a ruler. The player thought. They thought for a very long time, with the whole table watching.
The next card they played was the same one. The table held its breath.
"Disappointing," said the Headmistress, and let it stand.