What is surprising about the attitude of the two convicts towards one another?

Both the convicts - Magwitch and Compeyson - are sworn enemies and given half a chance they would immediately kill one another. In Ch. 3 both of them have escaped from the prison ships and are in hiding on the marshes waiting for a suitable opportunity to make good their escape. Naturally,they are both tense and nervous and scared of the slightest noise. Their imaginary fears makes them to over react even at the slightest noise or disturbance. This is what is surprising about their attitude and adds to the suspense, because the readers want to know more about the relationship of these two convicts. When Pip mistakes Compeyson for Magwitch and tries to surprise him by coming upon him from the behind unexpectedly, Compeyson imagines that some one has come to catch him and knocks down Pip and runs away. Similarly, when Pip gives the food and the file to Magwitch and tells him about Compeyson whom he had just then encountered, Magwitch becomes distracted and angry and in his revengeful mood begins to file away at his iron shackles so that he chase down Compeyson and kill him.