Mr Smith and his son Jim rent a boat from Mr Green. They find a very good place and catch a lot of fish. Now it is late and they are going home.

Jim says, "I'll come here again tomorrow."

The father laughs and says, "No, that's foolish! Mr Green won't give us the same boat next time."

"Yes, me too." say his father. "But how can we get back and find the right place again?" "I can make a mark on the side of the boat." Jim answers.