Riddle: What is the answer to selling paintings for free?

At the end of the Qing dynasty, there was a Taoist priest who traveled around. This Taoist priest is knowledgeable, can draw good pictures, and especially loves guessing riddles. One day, he came to Beijing. I think people say that Kyoto is full of talents, so I want to see it with my own eyes. So he drew a picture carefully. It's a black-haired poodle. This dog is vividly painted, especially its shiny black fur, which makes people full of praise. When the Taoist priest came to the downtown area, he hung the painting on the side of the road, which immediately attracted many pedestrians to watch. Someone bought this painting. The Taoist priest smiled and said, "I don't want to sell this painting, and I don't want to sell it at any price." There is a word hidden in this painting. If anyone guesses, I'll give it to him for free. "Hearing this, all the people in the world have such cheap things and a good white painting without spending a penny, so they are scrambling to guess. But after guessing for a long time, no one guessed right. At this moment, I saw an old man. He separated everyone, stepped forward, picked up the painting, rolled it up, picked it up, and left without saying anything. Everyone was shocked. The Taoist priest came forward and asked, "Old man, why did you take my painting before you guessed?" The old man kept silent and went out. Everyone also shouted, "Hey, don't take the painting yet, tell me what the answer is." The old man seems to be deaf, but he didn't say a word, just kept talking. When the Taoist saw this, he couldn't help laughing: "Bingo! Guess! "Why do you think the old man guessed it? Answer: It turned out that Taoist priests created a painting puzzle. The "black dog" in the painting means "black dog". "Black" and "dog" together, is the word "silent". So the old man was silent from beginning to end. No wonder the Taoist priest said he was right.