"Arms and the Boy" is a poem about World War I, so naturally there are bound to be weapons lying around. We tend to think of weapons as mere objects, and of the people who use them as the real bad guys (à la "Guns don't kill people. People kill people.") In the poem, though, the weapons—the bayonet-blade, the bullets—seem to take on a life of their own.
Lines 1-2: The speaker encourages the boy to feel his bayonet-blade. A blade can't actually be hungry, so we've definitely got some personification on our hands. But there's also a larger metaphor at work—one that compares the bayonet to a carnivorous animal.
Lines 3-4: The bayonet-blade is further described as "blue," or eager, and starving ("famishing") for human flesh. In this sense, the bayonet-blade is compared to some type of starving, murderous, and carnivorous animal.
Lines 5-6: The speaker tells somebody to help the boy stroke his "blind, blunt bullet-heads." Bullets don't have eyes, and can't technically be blind, nor can they "long for" (desire) something so this is yet another moment of personification.
Lines 7-8: The speaker describes a bullet cartridge with "fine zinc teeth." Teeth here is a metaphor for the bullets, which are sharp and used for killing. The repetition of the word "sharp" also reminds us of the wounds of war.