In The Boy in The Striped Pajamas, why did Herr Liszt begin coming to the house?

Bruno's family, in The Boy in The Striped Pajamas, has had to move from Berlin to what Bruno describes as a "desolate" place. Bruno and his sister Gretel have very little to occupy themselves and Bruno reflects on the unfairness of the situation.

After the family has settled in and Bruno's memories of Berlin are less prominent in his mind, Bruno's father decides that it is time to resume the children's education and Herr Liszt becomes their tutor. He has a propensity for the subjects of History and Geography and, whilst Bruno hopes that this will clear up his confusion about all the "great wrongs"done to him personally, it seems that Herr Liszt's preoccupation is with the "Fatherland."

Bruno is irritated by Herr Liszt's teaching and begins to reflect on his own recent past and becomes more curious about the people he sees in their striped pajamas compared to the men who visit his father in "uniforms of varying quality and decoration and caps and helmets with bright red-and-black arm-bands." So Bruno's desire to explore is reignited.