The Keaton Mask is a mask obtainable via the Anju And Kafei Quest. Kafei is seen wearing it at the begining of the first day. At night during the second day, if Link didn't save the old lady's bomb bag, Sakon will go to the Curiosity Shop and Kafei will follow him to his hideout. At 1 P.M. during the final day, if Link goes to the back of Curiosity Shop, he will find the man who owns the Curiosity Shop. Then he will give Link the Keaton Mask.
If Link wears this mask and if he cuts the grass that moves, Keaton will appear and if Link talks to him he will ask him five questions. If he answers all of the questions correctly, he will give Link a heart piece.