The lung has come in contact with Bile. This happens in the slaughterhouses when they are gutting the animals,  the gallbladder breaks and colors everything that it lands on.     Bile is not harmful , it is basically a digest aid, and is a bit alkaline and has this strong green pigment in it. Bile serves the purpose of breaking down fats in digestion. When dried it is not harmful at all , all the Lipase enzymes are deactivated but the pigment in the bile fluid is hard to wash away in the raw material, and becomes visible when the lung dries out. We strive to take these green pigmented pieces out during packaging , however it happen that we oversee and this goes in to the bag.