Fellow prisoners also tried to approach  Bonhoeffer, as soon as he could move about a bit more freely in the prison, the word quickly passing among them that he was someone whom it was good to know. They could meet him in the infirmary or during air raids and immediately afterwards. He began playing chess again and had a book on chess theory sent to him. He also revived, after many years, his gift for handwriting analysis. 

(Ferdinand SchlingensiepenDietrich Bonhoeffer 1906-1945: Martyr, Thinker, Man of Resistance, 343).