When Deckard Cain meets Rachael for the first time, she has an owl, and she claims it's real. He says "I thought they were extinct." She says no, you just can't buy them on the open market. He then tests his humanity detector on her, which she fails. They explain that she grew isolated on a spaceship leaving Earth which turned around and came home after the war, so she grew up without a sense of empathy. He is horrified to learn his detector may be flawed, and he may have killed real humans thinking they were androids. They then offer him the owl to cover it up. He finally realizes that they're lying and she's an android after all. He then says "And the owl?" "It's robotic, of course. Owls are extinct."

In the movie? He shows up and says "Nice owl, is it robotic?" Rachael goes "Yup, and so am I". Welp, there goes like 50 of the best pages of the book.

Another example, which really shows just how unnecessarily shallow the movie is: in the book, Rachael and Pris are identical model androids, and sex with androids is forbidden. The whole conflict Deckard experiences is based on the fact that he becomes infatuated with Rachael: not only is it extremely taboo, but his feelings start to interfere with his mission of killing her identical twin Pris. In the movie? Completely different replicants, and Pris is a standard-issue sex-bot. There's just no internal conflict at all.

Seriously people, read this book. It is fantastic.