During the conversation in the carriage, Mo Shanshan had been responding to Sangsang gently with "um-hum". When she heard Sangsang's last sentence, without hesitation she responded as usual, but then noticed something off. She raised the tone to express doubts and astonishment and some other complex emotions that were difficult to convey only through pitch fluctuation.
If it was a conversation between any other two women in the world, the conversation would be considered to be filled with tension and harsh irony, like they were confronting each other with daggers. But Mo Shanshan knew Sangsang so well that she knew Sangsang was just telling the facts and had no intent to show off.