Stimulated by the correspondence about oysters on my Comments page, I ordered a copy of Drew Smith’s book Oyster: a gastronomic history. Here I have learned more of what I did not know: that oysters have a heart; they are bisexual and can change sex during the course of a single season; they feed on plankton; food arrives through their lips and is extruded through their rectal chute; and the nutritional value of a dozen oysters is equivalent to that of a steak. The presence of oyster beds was crucial to prehistoric trade and over a million oyster shells were discovered while Silchester was excavated. Pepys ate oysters out of a (small) barrel and Dr. Johnson fed oysters to his cat. By the eighteenth century, there was a small industry round the oyster trade, particularly north of the Thames estuary, in Mersea, Brightlingsea and Mersea and, to the south, Faversham and Whitstable. But in the nineteenth century, when they were cheap, the oyster beds were destroyed by overfarming and, in the twentieth century, by disease and pollution. So, it’s good that the trade is being revived.