At about 15:50 mountain time, a Cessna 305A ground looped during landing rollout on runway 04 at the Winslow-Lindbergh Regional Airport. Neither the pilot/owner nor the flight instructor was injured. The owner had just bought the airplane and was ferrying the airplane to his home in Maryland. He did not yet have a taildragger endorsement, so the CFI was training him on the way. The instructor reported that the pilots landing was normal. However, when the pilot applied the toe brakes, his left shoe (size 14) slipped off the pedal and became jammed next to the console. The instructor stated that he yelled at the pilot to release the brake, but to no avail.