There is a sense in which the title of this poem could be viewed as focusing only on a part of the content of the poem: the poem is just as much about the reaction of the speaker and her companions to the snake as it is about the snake itself. However, when the poem is analysed in detail, it can be seen that the title can be read in a number of different ways.
On the one hand, it clearly relates to the snake as a predator. The description of the snake as it "quests" through the grass with its "Head down, tongue flickering on the trail" and hunts smaller prey is one that inspires fear in both the reader and the speaker. The description of the snake as "Cold, dark and splendid" highlights the horror he inspires, and his lethal nature as a predator. This poem is a description of a snake that is hunting, but the reader, and certainly the speaker identifies that if the snake had attacked them, it would have been a very dangerous and potentially lethal outcome for them.
However, the title could also be seen as being deliberately ambiguous, referring not only to the snake as a predator but to the actions of the speaker in trying to find a snake in its own territory. The response of the speaker and her friends throughout the poem is one of awe and shock as they are "frozen" by the sight of the snake that they recognise to be so deadly. Having wanted to encounter nature in its own environment, they have received considerably more than they bargained for, as the final two lines reflect:
We took a deeper breath of day,
Looked at each other, and went on.
The speaker and her friends seem to be shaken to have seen the snake and this is reflected in the "deeper breath of day" they take. They realise that hunting nature in its own territory is a risky business that reveals the true deadly characteristics of nature and the inherent fragility of man.