Epiglottis. The epiglottis is a flap of soft cartilage, covered by a mucous membrane. It is attached to the back of the tongue and acts as a valve during swallowing to prevent food and liquid from entering the lungs. This valve closes when we swallow food, liquid, even saliva, without us having to think about doing so.In other words, it is an unconscious action.t is attached to the back of the tongue and acts as a valve during swallowing to prevent food and liquid from entering the lungs. This valve closes when we swallow food, liquid, even saliva, without us having to think about doing so.