Ms Highsmith was potty about snails. She felt some kind of mystical communion with the things. No gastropod mollusc was safe from her kindly interest. She used to complain that humans were badly served by having "too little shell" to protect them againstthe world. Her later work, such as The Animal Lover's Book of Beastly Murder, featured ghastly fantasies about men being pursued by speeding Helicidae.
A harmless pursuit, you might think - after all, some people collect ceramic frogs - but her fascination bordered on the weird. According to a friend, she used to keep snails in her handbag and would, on a whim, take them out during dinner in posh restaurants and watch their nugatory progress across the tablecloth. Presumably leaving her fellow-diners demanding to know why the escargots cru weren't listed on their menus.