Who is the needle tip hidden in the brush head?

1. There is a needle hidden in a brush specially used to withdraw money. Click the pen, and the needle tip will leave a trace of passing.

2. The story comes from the time when Zhang communicated with the guards around him. It is common for a guard to take a letter to the bank to withdraw money. The loophole found by the guards was that Zhang wrote the number of silver dollars in his letter, which was too simple. After a long time, they came up with the idea of imitating notes. Many things happen, even he can't tell the truth. He stole writing paper from Zhang's case in advance and filled it in a quiet place, so he generously went to the bank to withdraw money. Unexpectedly, he can't be caught red-handed. Zhang personally questioned: Did you kill the guards? How to determine the authenticity, Zhang replied with a smile: simpleton, it turns out that there is a needle hidden in Zhang's special brush, and there are traces on the tip of the needle.