When Kafka first talks with Bizzlebek, he mentions that he read "That story about the Penal Colony". He is referring to the short story, "The Penal Colony". In it, Kafka describes the last use of an elaborate torture and execution device that carves the sentence of the condemned prisoner on his skin in a script before letting him die, all in the course of twelve hours.
Just before going to the Castle, Kafka ask Bizzlebek to burn his manuscripts if he never came back. Bizzlebek replies "such an extraordinary request". This is in reference of the real request Kafka asked his friend Max Brod before dying. Brod couldn't go with the request and had Kafka's work published.