I've had chicks pick at my scabs too, and try to eat my freckles until they bled (sharp beaks on those week old chicks). Adult hens will do the same thing. Any blood or sight of blood, and they will go after it. It's like a switch flips in their minds. So if anyone in your house hold ever gets bloody for any reason, once you stop the bleeding, be sure to cover the injury or paint it in Blu-kote (blue anti-pecking cream), or isolate the injured bird or something. I've heard sometimes they'll peck themselves, but mainly I've seen them peck others. It's a visual thing to do with the color red and/or the sight of blood.