What do Lombard and Vera discover at the end of the chapter Why is it significant?

What do Lombard and Vera discover at the end of the chapter Why is it significant? In their final confrontation, both Vera and Lombard accept it as a given that they are alone on Indian Island, and each assumes that the other is the killer. In a way, their behavior is irrational, since they should know that neither one of them could possibly have killed Blore.

In their final confrontation, both Vera and Lombard accept it as a given that they are alone on Indian Island, and each assumes that the other is the killer. In a way, their behavior is irrational, since they should know that neither one of them could possibly have killed Blore.