When Deckard asks Rachael if Tyrell's owl is artificial, she replies 'Of course it is'. However, her lips movements do not match what we hear. This is because when the scene was filmed, actress Sean Young answered the question by saying 'Of course not'. Director Ridley Scott changed this in post-production because he wanted to establish that Tyrell could make perfect imitations of living things.
When Rachael is playing, the keys she presses don't match the music we hear. The piano sound is in C major, but the picture shows her pressing black keys.