The poem makes heavy use of end-stopped lines, a formal feature that reflects the speaker's preference for short, direct statements without much adornment. For instance, he begins his narration in line 1 with one short sentence ("Today I am going to kill something.") followed by an even shorter one ("Anything.").
This pointed, forceful style continues as he describes his violent actions, as in lines 13-14:
I pour the goldfish down the bog. I pull the chain.
I see that it is good. The budgie is panicking.
The end-stops here, especially in combination with the caesuras in the middle of each line, give the impression that the speaker is narrating his actions in a matter-of-fact way, without reflection, emotion, or justification. His descent into psychopathy is thus reflected in the formal characteristics of the poem, particularly its use of end-stops.
Although end-stops are prevalent throughout the poem, they increase in number and cluster in intensity as the poem reaches its conclusion. While the earlier stanzas feature some enjambment, the fifth and final stanza has three end-stopped lines in a row. The final progression of actions is narrated entirely in end-stops, again with caesuras as well:
He cuts me off. I get our bread-knife and go out.
The pavements glitter suddenly. I touch your arm.
It is no coincidence that this is the climactic moment of the poem, in which the speaker seems to have graduated from killing animals to killing (or at least attacking) humans. As he becomes more violent and unpredictable, the language of the poem becomes correspondingly choppier. In this sense, the end-stop in the poem comes to reflect a world in which violence is inevitable, and in which the speaker takes irrevocable actions without consideration or empathy.