Why does magwitch jump with sudden fear when Pip points to where his mother is?

Magwitch jumps with sudden fear when Pip points to where his mother is because he is apprehensive about being discovered by the authorities. His past as a convict makes him highly anxious about being seen or recognized, especially in the presence of someone associated with Pip. This reaction underscores the tension between his desire to connect with Pip and the danger of his criminal background being revealed.