What is the face that Herbert sees in the fire

From the text, we can infer that Herbert's own face was among the horrible faces he saw.

He sat alone in the darkness, gazing at the dying fire, and seeing faces in it. The last was so horrible and so simian that he gazed at it in amazement. It got so vivid that, with a little uneasy laugh, he felt on the table for a glass containing a little water to throw over it. His hand grasped the monkey's paw, and with a little shiver he wiped his hand on his coat and went up to bed.