What unusual incident occurs at the local pub in Chapter 10 of Great Expectations?

Pip is sent by his sister to fetch Joe at the Three Jolly Bargemen, the local pub. There Pip finds Joe in the company of Mr. Wopsle and a stranger. When Joe greets Pip by his name, the stranger looks closely at him. Pip calls him a “secret-looking man,” though never having seen him before. The man wears a broad-brimmed hat, but underneath he wears a kerchief to hide that his hair has been shaved...

Pip is sent by his sister to fetch Joe at the Three Jolly Bargemen, the local pub. There Pip finds Joe in the company of Mr. Wopsle and a stranger. When Joe greets Pip by his name, the stranger looks closely at him. Pip calls him a “secret-looking man,” though never having seen him before. The man wears a broad-brimmed hat, but underneath he wears a kerchief to hide that his hair has been shaved off (as was usually done to convicts). The stranger keeps looking carefully at Pip all the while the men are talking, frequently nodding at him. When Joe is not looking, the stranger rubs his leg in an odd way and nods at Pip. He asks questions about the local area, especially about the marshes. The stranger then takes out a file and stirs his drink with it. With horror, Pip recognizes it as the file he had stolen from Joe and had given to the convict, Abel Magwitch. He realizes that this person knew the convict somehow. As Pip leaves, the stranger gives him a shilling wrapped in crumpled paper. At home, Pip discovers that the paper is two one-pound notes. Mrs. Joe wants to return the money immediately, assuming it was a mistake. The stranger has disappeared, however, so the money haunts Pip in fear that the convict will return.