The answer is: how hot the spear is.
An epic simile, or Homeric simile, is a comparison between something familiar or ordinary and something strange. It is usually many lines long and it helps the reader make the scene described, usually at moments of turmoil or battle, more vivid. In the epic simile above, Homer makes the reader understand how hot the spear that blinds the cyclops is by comparing the eye of the cyclops to a cold tub as the spear that blinded him penetrates it, just like a piece of metal would enter a tub in order to be molded.
