Silence spreads like an epidemic in this poem, and the speaker treats it as something deadly, a "black death" that settles over everyone. People have lost their inner fire, and the eagle that "preys on everyone's sanity" suggests a constant, picking-away pressure on the mind. Even though lightning and voices rage inside their heads, nobody speaks. The silence has "sealed their lips," which echoes the muzzle in the title.
Then the focus narrows to one girl. She closes her eyes and breaks the seal, an act that looks quiet but is clearly decisive. The final line, "She is ready," is short and stark, and it reads as determination rather than fear.
The mood begins bleak and suffocating, with heavy images of disease and predation. By the end it turns tense and defiant, as if something is about to happen. The poem seems to be about finding your voice when everyone around you is holding theirs back.