Matthew Chernov “They were reality TV before it existed.” That’s how Matt Singer, author of the upcoming book “Opposable Thumbs: How Siskel & Ebert Changed Movies Forever,” describes the two most famous film critics in history. Like countless fans of his generation, Singer – whose book will be published by Penguin Random House on Oct. 24 – credits Siskel and Ebert with stoking his love of cinema at a young age.