I'm guessing they rotted, very slowly

The Scotsman has a decent profile of Kazuo Ishiguro.
And, from The Independent:
"Kazuo Ishiguro's first memories of England are of double-decker buses and squashed hedgehogs. "These were the exotic things," he tells me. "I remember the branches scraping against the roof of the bus and looking down at the puddles and the squashed hedgehogs and feeling that they were all in some way connected. What", he asks suddenly, "happened to the hedgehogs?"