we lie down screaming as rain punches through (line 7)
This loud passage, in an otherwise quiet poem, sticks out not only because it's right at the beginning, but because we're not entirely sure what's causing the screaming. It could be that the Haitians are being killed by Trujillo (or his men). Violence is implied even in the way the rain is falling – not so much falling as "punching." So the overall effect becomes that of a group of people screaming while being physically abused.
And we lie down. For every drop of blood there is a parrot imitating spring. (lines 17-18)
This passage begins in the same way as the quote above ("we lie down"), but its proximity to the drops of blood indicate that there is more to read here than, say, settling down to take a nap. The interesting thing about this quote is the comparison inherent in it – the poem implies that, for every violent act, there is something beautiful. So while Haitians are dying en masse, the parrot continues to do its thing, oblivious to the condition of the world in which it exists.
As he paces he wonders Who can I kill today. (lines 29-30)
This thought comes directly after we are given a picture of Trujillo thinking about his mother, which sets up a causal relationship between his mother's death and Trujillo's incredible propensity for violence. It's almost as if the only way he can think through his mother's passing is by thinking about causing the deaths of thousands of others. If this kind of behavior is hard to wrap your brain around, we understand. But that's not a bad thing. It probably means you're not a psychopath.