The sea-girl's face had dimpled all over with fun.

Colts and other animals cannot laugh at us, else we might not be so peaceful in our assumption that they never criticise.

Caius before this had always supposed himself happy in his little efforts to please children and animals; now he knew himself to be a blundering idiot, and so far from feeling vexed with the laughing face in the water, he wondered that any other creature had ever permitted his clumsy caresses.
Having failed once, he now knew not what to do, but stood uncertain, devouring the beauty of the sprite in the water as greedily as he might with eyes that were not audacious, for in truth he had begun to feel very shy.
"What is your name ?" he asked, throwing his voice across the water.
The pretty creature raised a hand and pointed at some object behind him.
Caius, turning, knew it to be the epitaph.

Yes, that was what his own intelligence had told him was the only explanation.
Explanation?
His reason revolted at the word.

There was no explanation of an impossibility.