What does Paul's mother find on returning home?

From the text:

Softly, frozen with anxiety and fear, she turned the door-handle.

The room was dark. Yet in the space near the window, she heard and saw something plunging to and fro.

She gazed in fear and amazement. Then suddenly she switched on the light, and saw her son, in his green pyjamas, madly surging on the rocking-horse. The blaze of light suddenly lit him up, as he urged the wooden horse, and lit her up, as she stood, blonde, in her dress of pale green and crystal, in the doorway.

"Paul!" she cried. "Whatever are you doing?"

"It's Malabar!" he screamed in a powerful, strange voice. "It's Malabar!"

His eyes blazed at her for one strange and senseless second, as he ceased urging his wooden horse. Then he fell with a crash to the ground, and she, all her tormented motherhood flooding upon her, rushed to gather him up.