And the monkey, having attained his lofty and gigantic body like unto a mountain, furnished with coppery eyes, and sharp teeth, and a face marked by frown, lay covering all sides and lashing his long tail. And that son of the Kurus, Bhima, beholding that gigantic form of his brother, wondered, and the hairs of his body repeatedly stood on end. And beholding him like unto the sun in splendour, and unto a golden mountain, and also unto the blazing firmament, Bhima closed his eyes.

In plain words: Hanuman's body becomes like a mountain, with copper-colored eyes, sharp teeth, a frowning face and a long swishing tail. Bhima is amazed and gets goosebumps. Hanuman shines like the sun, so Bhima has to close his eyes.