Tang Bohu joke?

According to legend, Tang Bohu once sold paintings in the street. One day, he hung an ink painting with a black dog on it, which was very cute. Tang Bohu said to people, "This is a crossword puzzle, and the buyer needs to pay thirty taels of silver. If he guessed the riddle, he wouldn't charge a penny. " Most of the day passed, and no one guessed. At this moment, a young man said, "I guessed right." "Tang Bohu asked him to tell the answer, but he just smiled, took down the picture and went away.

Tang Bohu looked at the young man's back and said with a smile, "Bingo! He understands! "

Can you guess what this word is?

Silence = black dog = black dog