This is one of those Zen koans that make you say "Huh?":
While Seisetsu was the master of Engako in Kamakura he required larger quarters, since those in which he was teaching were overcrowded. Umezu Seibei a merchant of Edo, decided to donate five hundred pieces of gold called ryo toward the construction of a more commodious school. This money he brought to the teacher.
Seisetsu said: “All right. I will take it.”
Umezu gave Seisetsu the sack of gold, but he was dissatisfied with the attitude of the teacher. One might live a whole year on three ryo, and the merchant had not even been thanked for five hundred.
“In that sack are five hundred ryo,” hinted Umezu.
“You told me that before,” replied Seisetsu.
“Even if I am a wealthy merchant, five hundred ryo is a lot of money,” said Umezu.
“Do you want me to thank you for it?” asked Seisetsu.
“You ought to,” replied Umezu.
“Why should I?” inquired Seisetsu. “The giver should be thankful.”
From "Zen Flesh, Zen Bones" by Paul Reps.
What's your take on this one?