《太平广记·卷九十九·释证一》
突然遇上一只蛤蜊，无论怎么敲打都开不了，皇帝很奇怪，把它放到了桌子上。
忽有一蛤，椎击如旧，帝异之，安置几上。
Suddenly, he runs into a clam that cannot be opened no matter how much he bangs on it. The emperor finds it strange and leaves it on the table.