Director Sir Ridley Scott and director of photography Jordan Cronenweth achieved the famous "shining eyes" effect by using a technique invented by Fritz Lang and his cinematographer Eugen Schüfftan known as the "Schüfftan Process": light is bounced into the actors' and actresses' eyes off a piece of half-mirrored glass mounted at a forty-five-degree angle to the camera.
Joanna Cassidy (Zhora) was at ease with the snake around her neck because it was her pet, a Burmese python named "Darling".
Rutger Hauer came up with many inventive ideas for his characterization, like the moment where he grabs and fondles a dove. He also improvised the now-iconic line "All those moments will be lost in time... like tears in rain". He later chose "All those moments" as the title of his autobiography.
(at around 38 mins) After Pris (Daryl Hannah) first meets J.F. Sebastian (William Sanderson), she runs away from him, skidding into his car and smashing the window with her elbow. This was a genuine mistake caused by Hannah slipping on the wet ground. The glass wasn't breakaway glass, it was real glass, and Hannah chipped her elbow in eight places. She still has the scar from the accident, as can be seen in Dangerous Days: Making Blade Runner (2007), the "making of" documentary of this movie.
Ridley Scott: [opening scroll] The movie opens with a scroll about the replicants and the Blade Runners.