Joke Collection Website - Cold jokes - What does "knocking joke" mean?

What does "knocking joke" mean?

A: "What are you doing with tape?"

B: "Don't mention it. When I bought rice in the morning and found a broken one-dollar bill, I wanted to buy tape to stick it on. "

A: "Then why not insist?"

B: "I spent that one yuan when I bought the tape, and now I don't know what to do."