This is a short story from Aesop’s Fables. A merchant and his donkey travelled to the sea to carry some cheap salt to sell in the mountains. On their way back, the donkey slipped and fell into the water while they were crossing a stone bridge. As the donkey struggled to get up, the water washed off the weight on his back. The donkey noticed the difference and on their second trip, he pretended to slip. The donkey was happy, but the merchant wasn’t. He had already lost two sacks of salt! The merchant soon figured out what went wrong and decided to trick the donkey. On their third trip, the donkey pretended to slip once again, but just as the sack touched the water, it became heavier! What a clever merchant! Do you have any idea what was on the donkey’s back?