Successful vs. unsuccessful techniques for starting a conversation with a stranger about their book

Man I do not know, interrupting me as I was reading on the train today: "What's your book about?"

Me, wondering why people interrupt strangers to ask what a book whose title they don't even know is about when the answer can't possibly have any more meaning to them than selecting a random ISBN and Googling it, while I also tried to figure out how long a description someone who can't actually care wants and whether that description should be plot-based or thematic, and finally deciding to whittle down Elizabeth Gaskell's excellent 446-page North and South to one sentence fragment: "Ummm… Class conflict, gender relations, moral responsibility vs. the exertion of one's own human rights, how a free market works, and the right to assert one's independence in mid-1800s England…."  (I suppose I could have gone with the far more interesting-sounding and equally true "a man and a girl-almost-woman disagree about everything under the sun, which makes him fall in love with her and makes her hate him, and 400 pages later after she becomes rich and everyone else in the book dies, she grows up and falls in love with him, and it's awesome because their entire relationship is based on having long discussions where they do nothing but passionately disagree with each other about politics and world views while always listening respectfully," but somehow the shorter, boring, admittedly uninviting answer is what came out.)

Him: "England?"

Me: "Yeah"  [still making eye contact, wondering if this was the end of the conversation and I should go back to reading or if I was supposed to either say something more or wait for him to say something]

Him: "Huh"

Me: [slowly and awkwardly returning to my book, wondering what possible variations in this dialogue could have produced less uncomfortable results for both of us]

But then there was the guy I didn't know who interrupted my reading Hatchett with "Hatchett! That's a blast from the past!  Doesn't the poor kid have to go through that all again in another book, too?" and I wound up having a long, interesting conversation with him... about the evolution of the English language and how English is taught in our education system.

The moral of the story?  If you're going to interrupt someone you don't know to ask about the book they're reading… it might help to have a follow-up sentence.  And if you're on the receiving end of the question about your book... Well, just hope you're not reading Dickens's The Pickwick Papers.