Metaphors and similes help identify one thing by relating it with another. Similes use the words "like" or "as," whereas metaphors link them directly in various ways, such as personifying inanimate objects with human qualities. In Dickinson's poem, they give insight as to how the speaker sees nature. For example, "He glanced with rapid eyes/ that hurried all around." So even before you read the next two lines, you can picture the quick movement of the bird's eyes as it studies its surroundings. Once you read, "They looked like frightened Beads, I thought --/He stirred his Velvet Head," you find the use of the simile "like frightened Beads" to specify the birds' potential reason for its action. The bird's head is not literally made of velvet, but the simile illustrates it as smooth, silky and perhaps red or blue in color.