Simple categories matching mucous:

• membrane,
• tissue,
• surface,

Members with property mucous:

• digestive_tract,
• eye_conjunctiva,
• mouth,
• gum,
• gastrointestinal_tract,
• oral_mucosa,
• adenoid,
• conjunctiva,
• eyes,
• respiratory_tract,
• urinary_tract,
• cornea,
• tonsil,
• bladder,
• eyelid,
• skin,
• throat,
• genitourinary_tract,
• eyelid_conjunctiva,