Tyson had furnished him with a key to his wife's moods.

Moreover, a simpler explanation had occurred to him.
Mrs.Nevill Tyson was fond of driving; she had been forbidden to drive, therefore she drove; she had never driven any animal in her life before, and, notwithstanding her inexperience, she had accomplished the dangerous feat without injury to anybody.

Hence no doubt her laughter and her triumph.
But this again was symbolism.

He determined to sleep on it..