who does vera think the sixth line of the poem implies is the murderer? why?

Vera tells them that she thinks they are both idiots and reminds them of the rhyme: “Four little Indian boys going out to sea; / A red herring swallowed one and then there / were three.” She tells them that the “red herring” is the clue. Armstrong’s disappearance is just something to distract them. Thinking of the next verse in the rhyme, Blore tells her that since there is no zoo on the island, the killer will have difficulty pulling off the next killing. “’Don’t you see?’” Vera says. “’We’re the Zoo…Last night, we were hardly human any more.” She believes the killer is Armstrong.