Sentence:  Two clotted balls the color of <WSD>mucus</WSD> rolled between fiery lids . 
Meaning of the word marked with <WSD> tags:  protective secretion of the mucus membranes; in the gut it lubricates the passage of food and protects the epithelial cells; in the nose and throat and lungs it can make it difficult for bacteria to penetrate the body through the epithelium