Why did Holden need to VK Leon, if the police knew what he looked like?

This test is more crucial in the novel, where it is intimated that there are humans who have actually been replaced by look-alike replicants.

Replicants, however, can readily change their appearances and aren't easily recognized from photographs, e.g., Zhora's tattoo, and Pris' raccoon makeup. In the July 1980 screenplay, Deckard muses, "They could change their appearances but not their future."

In the December 1980 screenplay, Deckard says Zhora's "black hair is a wig which now hangs on the wall next to the shower. She didn't look like Nexus designated Zhora to begin with, but even less now."

Bryant tells Deckard that there were six replicants, three male, three female. Obviously, Roy and Leon are two of the males, and Pris and Zhora are two of the females.

Bryant also says that "one of them got fried trying to get into the Tyrell building", but doesn't specify the sex.

That leaves one replicant, either male or female.

It has been hypothesized that Deckard was the sixth replicant, but there is ample evidence that this is not the case.

In an earlier version of the script "Mary" was the fifth replicant, and "Hodge" was the sixth. Bryant's line in that script got past the screenwriter unnoticed.

It was recorded correctly in the Workprint as "two got fried" but botched again on the release print.

Why is it so difficult to tell a replicant from a human, when replicants can put their hands in boiling/freezing liquids without damage?

Surely a tissue sample would suffice?

Perhaps, but Holden couldn't even get a straight answer from Leon, much less a tissue sample.

How did word of Rachael's escape get out so quickly, and how could Tyrell tell that she had gone for good?

Remember that Deckard called Rachael at home while he was still at the nightclub.

It could not have been more than a couple hours before he gave chase to Zhora. (How long could she "take the pleasures from the serpent"?) Was that enough time for Rachael to run away then for Tyrell to call the police and have Bryant put Deckard onto her?

Another explanation is that Tyrell's "experiment" was voided when Rachael discovered she was a replicant;

Tyrell simply used this opportunity to dispose of her.

How did Roy get into Tyrell's office so easily?

Did Tyrell trust Sebastian enough to give him the option of bringing anyone/anything up in the lift?

Tyrell was unaware there was anyone in the lift with Sebastian until he said "I brought a friend."

In earlier scripts, Sebastian and Chew both held the highest security clearance.

In an early version of the script, Tyrell was a replicant, and Roy picks up on this because of a key both Sebastian and Tyrell are wearing.

In that version, the real Tyrell was in a "cryocrypt", for sketches of which see "The Blade Runner Sketchbook".

After Roy kills the replicant Tyrell, he makes Sebastian show him the crypt where the real Tyrell lies dead because of a mistake Sebastian had made.

Technical
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Norwegian subtitles translate "Sushi That's what my ex-wife called me. ColdFish."

into "Sushi, my wife, used to call me a cold fish.

"Swedish subtitles spell Roy's name "Beatty", translate Deckard's license number from 260354 to 26354, and (in BRDC) "C-beams" to "seabeams".

Norwegian subtitles translate Deckard's license number from 260354 to 26354.

The theatrical version dubbed into German translates "hardcopy" (from the Esper machine) into "solid copy", but in BRDC, it is "printout".

Italian-dubbed versions translate "C-Beams" to "B-Beams" and Tyrell's line"...and you have burned so very, very brightly..." to "...and you haveburned your candle from both ends...".

Leon's "Nothing's worse than havingan itch you can never scratch" becomes "Nothing's worse than living in terror."

Gaff's "...but then again, who does?" becomes "If this can be called living..."

Both the 1982 release and BRDC are incorrectly dubbed into Spanish: they translate the "shoulder of Orion" to the "shores of Orion".

The original Danish video release had "off-world" translated as "subterranean".

The Japanese neon sign for "gorufu you-hin" (golf equipment) has the wrong character for "you": it is missing a verticle stroke, creating "getu" (moon).

The last thing the Sushi Master says is "wakatte kudasai yo" ("please understand my position"), an odd thing to say at that time.

In the very first shot of Batty, we see his hand clenching up. If you look carefully as he turns his hand just before the shot changes, you can see the nail sticking through the back of his hand (Criterion CAV laserdisc: frames C-07 37124 and 37125).

He doesn't actually insert that nail until later in the film.

Also, in the same scene, though Roy is supposedly alone (in a phone booth) you see someone's hand on his shoulder. This is actually from a later scene with Tyrell, shown in mirror image.

Gaff and Deckard fly past the same rooftop twice on their way to see Bryant.

During the VK test, Leon says "My mother... let me tell you about my mother", but when Deckard recalls this on his way to his apartment, Leon's voice says "I'll tell you about my mother!" This is probably Scott playing with the audience's memory the way Tyrell trifles with Deckard's.

The snake tattoo on Zhora only appears after the Esper machine has stopped zooming, and when it produces a hard copy, Zhora's face is at a different angle to that on the screen.

The wording on the Million Dollar Movie marquis outside Sebastian's apartment changes.

When the Cambodian woman puts the snake scale into the electron microscope, she doesn't take it out of the plastic bag. We should be looking at a picture of a plastic bag.

The serial number that she gives Deckard is not identical to the one in the image.

Additionally, the image is not a snake scale, but a female marijuana leaf [see Scharf's book in section 7].

When Deckard goes to Ben Hassan's (the snake dealer), their lip movements do not match the dialog.

Although correct in the Denver/Dallas Sneak, the take wasn't deemed satisfactory for other reasons. The mismatch was a compromise.

When Zhora goes crashing through the plate-glass windows, the stunt double looks nothing like the actress, her wounds disappear and reappear, and she is wearing flat-heeled boots rather than the high-heeled ones she put on in her dressing room.

The sounds of the bullets hitting her body doesn't correspond to when she is visibly hit.

Also, you can see her holding the trigger-ball and tube for the bloodbags she is carrying.

When Leon throws Deckard into the car window, the window was already broken. This is not necessarily a goof.

In all versions of the film, events occur in the following sequence: Deckard kills Zhora and then buys a bottle of Tsing Tao.

Gaff takes him to Bryant. Deckard then spots Rachael and tries to catch her but gets beaten up by Leon.

When the script included Mary (another replicant), the sequence ran as follows:

Deckard kills Zhora and then spots Rachael looking on. He chases Rachael, only to be beaten up by Leon. After Rachael kills Leon, Deckard buys a bottle of Tsing Tao and has to warn her with a glance when Gaff approaches. Gaff takes him to Bryant, who tells him that there were "four to go" (Roy, Pris, Mary, and Rachael).

When they eliminated Mary from the script, they had a problem:

Bryant should say that there were "three to go" (Roy, Pris, and Rachael).

Instead of reshooting this scene, they moved it and the scene of Deckard buying Tsing Tao ahead of Leon's death, so that the "four to go" would be Roy, Pris, Leon (not Mary), and Rachael.

They nearly got away with this, but are now a few problems:

1) When Deckard is talking to Bryant, he shows wounds from his fight with Leon, although he hasn't had the fight yet.

2) Since he now buys his bottle before he fights Leon, it should be there while he's chasing Rachael and fighting Leon (it's not). The bottle mysteriously reappears when he gets back to his apartment.

This problem is purely the result of Bryant telling Deckard, "I've got four skin jobs walking the streets" but only accounting for 1 of the remaining 2.

When Pris steps out of Sebastian's elevator, her hair is dry, but when she is inside the apartment, it's wet again.

Support cables are visible whenever you see a closeup of a spinner floating above a city street. The cable is most visible when Gaff departs with Deckard in the beginning of the movie. There is a close-up of the spinner rising in the rain and the line is very visible where it connects to a fender.

Later when a cop floats down to Deckard sitting in his car and asks his business, you can spot the cable if you look closely.

Pris' raccoon makeup changes slightly three times.

Rachael's makeup changes throughout the love scene.

A gunshot wound is visible before Pris is shot.In the Deckard/Batty confrontation, after Deckard has been given his gun back and stalks off, you can spot the shadows of the cameraman, gaffer, and the camera on the wall.

When Batty is holding onto Deckard's arm, Deckard's shirt is untucked.

When he is thrown down, the shirt is tucked in.