what was the narrator's friend's experience at his first punting

J. lists the different types of rowing and the pitfalls that novices face when they attempt to row for the first time. He discusses punting, a type of rowing where the passenger stands up in the boat and propels it along using along using a long pole that is pushed against the riverbed. However, this type of rowing is hazardous for beginners; J. describes a friend who was not paying attention and stepped off the boat, leaving himself clinging to the pole in the middle of the river as the boat drifted away. On another occasion, J. and his friends noticed an amateur punter having trouble keeping control of his boat. Thinking it was someone they knew, they made fun of him brutally until they realized that the man was, in fact, a stranger. Harris had a similar experience when a stranger thought he was a friend and began roughhousing with him while swimming.