The snake in this poem isn't lying in the grass. It lives in a person's eyes. The speaker describes something dangerous that hides or waits, then shows itself "when least expected." The glitter in the eyes suggests a hidden hostility: someone who seems harmless but is quietly watching for a chance to strike.
The poem never says who this person is, and that vagueness is part of its effect. It could be an enemy, a false friend, or anyone whose smile can't be trusted. The speaker seems wary and uneasy, as if they have learned that danger often looks calm at first.
The mood is tense and watchful. The short, broken lines make us wait, much like the snake does, and the final image of the fangs being revealed arrives with a small jolt. The poem ends just as the threat comes into view, leaving us with the feeling that the danger is real and close.