It is a reaction from frivolity.
I suppose that I am over-enjoying life; that is all." She laughed, using her fan, although the place was cool enough and they had not danced long.

To and fro flitted the silken vanes of her fan, now closing impatiently, now opening again like the wings of a nervous moth in the moonlight.
He wished she would come to her point, but he dared not lead her to it too brusquely, because her purpose and her point were supposed to be absolutely hidden from his thick and credulous understanding.

It had taken him some time to make this clear to himself; passing from suspicion, through chagrin and overwounded feeling, to dull certainty that she, too, was using him, harmlessly enough from her standpoint, but how bitterly from his, he alone could know.
The quickened flutter of her fan meant impatience to learn from him what she had come to him to learn, and then, satisfied, to leave him alone again amid the peopled solitude of clustered lights.
He wished she would speak; he was tired of the sadness of it all.
Whenever in his isolation, in his utter destitution of friendship, he turned guilelessly to meet a new advance, always, sooner or later, the friendly mask was lifted enough for him to divine the cool, fixed gaze of self-interest inspecting him through the damask slits.
Sylvia was speaking now, and the plumy fan was under savant control, waving graceful accompaniment to her soft voice, punctuating her sentences at times, at times making an emphasis or outlining a gesture.
It was the familiar sequence; topics that led to themes which adroitly skirted the salient point; returned capriciously, just avoiding it--a subtly charming pattern of words which required so little in reply that his smile and nod were almost enough to keep her aria and his accompaniment afloat.
It began to fascinate him to watch the delicacy of her strategy, the coquetting with her purpose; her naive advance to the very edges of it, the airy retreat, the innocent detour, the elaborate and circuitous return.

And at last she drifted into it so naturally that it seemed impossible that fatuous man could have the most primitive suspicion of her premeditation.
And Plank, now recognising his cue, answered her: "No, I have not heard that he is in town.

I stopped to see him the other day, but nobody there knew how soon he intended to return from the country." "I didn't know he had gone to the country," she said without apparent interest.
And Plank was either too kind to terminate the subject, or too anxious to serve his turn and release her; for he went on: "I thought I told you at Mrs.Ferrall's that Mr.Siward had gone to the country." "Perhaps you did.