Answer:
What the simile adds to this passage is:
* a comparison between the sea and a cauldron
* a visual representation of the sea’s anger
Explanation:
The question is not complete since it does not provide the passage, here is the passage:
In travail, sobbing, gaining on the current,
we rowed into the strait – Scylla to port
and on our starboard beam Charybdis, dire
gorge of the salt sea tide. By heaven! when she
vomited, all the sea was like a cauldron
seething over intense fire, when the mixture
suddenly heaves and rises.
This passage from the Odyssey gives a very extensive and complete description of the elements that are part of the simile, by making the comparison of elements it also provides a very visual and clear representation of the sea, one of the key parts is the use of the line "all the sea was like a cauldron"