so it is true - they serve chowder on London mass transit? Pip pip.
But, what I was really getting at, although I guess it wasn't clear, is why in the devil is it called an Oyster card?
I went and chucked it in the goog:
The Oyster name was agreed on after a lengthy period of research managed by TranSys and agreed by TfL. Several names were considered, and Oyster was chosen as a fresh approach that was not directly linked to transport, ticketing or London. According to Andrew McCrum, now of Appella brand name consultants, who was brought in to find a name by Saatchi and Saatchi Design (contracted by TranSys), Oyster was conceived and promoted because of the metaphorical implications of security and value in the component meanings of the hard bivalve shell and the concealed pearl, the association of London and the River Thames with oysters, and the well-known travel-related idiom "the world is your oyster".