El General searches for a word; he is all the world there is. (lines 4-6)
The image implied here isn't so much concrete as it is cerebral (that is, something going on in someone's head) – we see Trujillo mulling over what word he's going to use to test whether or not someone is Haitian. If they fail that test – as we know from the epigraph – they will die. Just the simple fact that he can do this at all implies the amount of power he has over these people; it causes them to view him as all-encompassing, as "all the world there is."
El General has found the word: perejil. Who says it, lives. He laughs, teeth shining (lines 13-14)
This quote is really just an extension/specification of the quote above it – it makes the situation more explicit, in other words. We sort of know what's going to happen when Trujillo is searching for a word, but now we know both exactly what that word is and exactly what his plan will be for those who can't pronounce it. We're told all this in the epigraph, but having it in the story – adding his laugh, and his teeth (very animal-like, at that) – make it a part of the poem itself, rather than just a peripheral fact.
The cane appears in our dreams, lashed by wind and streaming. (lines 15-16)
We shift, here, from looking (poetically, that is) at what Trujillo is doing to what the Haitian sugarcane workers are doing. This is also an expression the power dynamic in the poem. The Haitians cannot escape their slavery, even in their dreams; the sugarcane haunts them and the verbs that Dove uses – namely "lashed" and "streaming" – further reinforce the master/slave relationship, even though those verbs are technically attached to the sugarcane. (We like that move, by the way – it's kind of subtle and creepy.)