What incident does Douglass narrate to indicate why slaves often gave seemingly contented replies when asked about their treatment?

Colonel Lloyd was very wealthy and had more slaves than he actually had seen. One day he sees a slave on a road that belonged to him. He asked how he is being treated and the slave told the truth. He said that he was overworked and ate little. The Colonel beat him. This is why it is wise fore a slave to show he is contented.