The likeness between the twins was apparently weighing on her mind--an unsolved problem that vexed and irritated it.

Without anything said by me to lead to resuming the subject, she returned obstinately to the assertion that she had just made.
"I tell you again I am sensible of a difference between them," she repeated--"though you don't seem to believe me." I interpreted this uneasy reiteration as meaning that she was rather trying to convince herself than to convince me.

In her blind condition, it was doubly and trebly embarrassing not to know one brother from the other.

I understood her unwillingness to acknowledge this--I felt (in her position) how it would have irritated me.

She was waiting--impatiently waiting--for me to say something on my side.