Possible Clues:

• Mollusks with hinged shells
• Molluscs with hinged shells
• Clams and oysters, e.g
• Mollusks with two shells hinged together
• Is that the way radio used to work for Molly Malone, by the sound of them?
• Oysters, clams and others with hinged shell
• Shellfish with hinged double shells, like oysters
• Oysters, clams, cockles etc
• eg Oysters