Excellent movie .. didn't understand one part (.. SPOILERS.. )

The movie was well made and worth a watch.
The only thing we didn't understand is ( SPOILERS ahead )
.. in the end when they are talking and he says under his breath that she doesn't understand Malayalam. He says to say "Bhaaa" not "Faaa". Then she has this guilty conscience , with the background music rising as if she got caught !!! She walks into the bathroom and remembers what all he had said from the beginning of the movie .... so what was all that about ????????????????????? What is she hiding ???? Is she not Mallu ??? Why does she focus on the point about his mother being a nurse from Kottayam ?????