very calm. A variation of the phrase happy as a clam at high tide, which comes from the fact that clams, considered a delicacy in America, are gathered only at low tide. In other words, a clam would be happy at high tide because it would not be being gathered for food. Similarly, oysters withdraw into their shells when the tide goes down. So, an oyster would be very calm in high tide. —PDC Volume 6 Approved Glossary