Two men were sitting together on a ship. They were on a long travel. One of them was a professor. The other was a farmer. They sat without talking for a while, and then the farmer said, "Let's do something to pass the time." "What do you want to do?" the professor asked. "We can ask each other riddles." The farmer said, "You start." "Let's make the rules first," the professor said. "That's not fair. You are a professor with much knowledge. You know more things than I do. I am just a farmer." "That's true." The professor said. "What do you want we should do?" "If you don't know the answer to a riddle, you pay me $100. And if I don't know the answer, I'll pay you $50." The farmer said. The professor thought about this, then he said, "OK. That's fair. Who will go first?" "I will," The farmer said. "Here is my riddle. What has three legs when it walks, but only two legs when it flies?" The professor man repeated the riddle, "What has three legs when it walks, but only two legs when it flies? Mm, that's a good one. I'm afraid I don't know the answer." He gave the farmer $100, then said, "Tell me the answer. What has three legs when it walks, but only two legs when it flies?" "I don't know." The farmer said and gave him $50. The story took place   _  .
on a farm between two passengers before a long plane journey in a shop