The Dog & The Knife

Just wondering if folks have noticed the connection between the start of the movie when Walter is bitten by the dog NED and towards the end of the Movie with the reveal that he is Laura's murderer?

During that flashback scene I'm pretty sure Laura has the knife and strikes Walter on the left forearm...the same spot that NED bites him in the opening scene!

Which has me asking the following questions:

1)Did Walter have to be bitten for the plot to unravel?

2) Of all the second hand and charity bin stores on the planet how did the 1 copy of the 23 book find it's way into a bookshop in Walter's neighbourhood?

3)If, as some folks have suggested, that the Doctor went crazy after having obsessed over the book, why didn't Walt's wife have any such obsessive feelings? Afterall, she'd read much more of the story before W. But more's to the point, as the book is Walt's story why would anyone other than Walt feel some kind of obsessive behaviour due to this story? Agatha seemed level headed especially when she gave Walt spoilers that Fingerling was a baddy. So was the Doctor just a crazy guy and is the movie suggesting that all Psycho Doctors are Psycho?

4)Sorry, but how contrived were NED's appearances. Middle of the road? C'mon! He would have been road kill by lunchtime!

Thanks for any comments. Cheers.