How we cite our quotes: All quotations are from Blade Runner.
Quote #1
TYRELL: She's beginning to suspect, I think.
DECKARD: I don't get it, Tyrell. How can it not know what it is?
Deckard is still thinking of the replicants as things—indicated by the fact that he refers to Rachael as "it." He hasn't observed the genuine humanity of the replicants yet, and he's puzzled by the fact that Rachael seems so real.
Quote #2
RACHAEL: May I ask you a personal question?
DECKARD: Sure.
RACHAEL: Have you ever retired a human by mistake?
DECKARD: No.
RACHAEL: But in your position that is a risk...
TYRELL: Is this to be an empathy test?
Even though Rachael isn't a human, she's questioning Deckard's own sense of empathy. She's hinting that a failure of empathy might be at work in his own view of things, since he makes his living by killing escaped replicants, who are nearly identical to humans.
Quote #3
TYRELL: Rachael is an experiment, nothing more.
RACHAEL: You know that Voigt-Kampff test of yours? Did you ever take that test yourself?
Rachael is questioning Deckard's own sense of identity. How does he know he's not a replicant with implanted memories? Could he pass the test he's administered to her? Given some interpretations of the movie, Rachael's suggestion might be right on: it's subtly hinted at different moments that Deckard might actually be a replicant.