Large shellfish. "Like mussel" is a kind of large shellfish that lives in fresh water. It generally lives in rivers and lakes. It looks like a clam, but it is bigger, sometimes reaching dozens of kilograms. Because of its hard shell, pearls or other treasures are often hidden inside, so it is often caught by human beings. In Chinese, "like mussels" is often used to describe precious objects inside things or treasures in people's inner world, which need to be obtained through certain efforts and excavation.