Signs that a novel may not be holding your attention

• When it takes you several days to read a reasonably short book written in what ought to be pretty straightforward prose.
• When a character who was apparently introduced earlier shows up many chapters later and, like David Spade on Saturday Night Live, you want to say, "And you are ---? And this is regarding ---?" 
• When this character has somehow acquired a new name, thus explaining part of the confusion, and you find this infuriating.
• When a character refers to "that passionate night in Paris" and you think, wait, what? Was that in this book?
• When you start resenting the introduction of yet another character because you want to know if this one has a point or is just going to be thrown in the corner with the other pointlessly introduced characters. 
• When you start to think about the characters and drift off into a microburst of sleep and dream a more gripping plot than the one you've been reading, only to come back to reality and characters that you can't remember.
• When the author writes a passage that really does make this sound like a classic, if a forgotten one, only to lose the thread in the next chapter.
• When the twists of the plot are such that the movie Anonymous makes sane historical sense by comparison. (To paraphrase Chinatown: "My son! My brother! My lover!")