20 Things You Somehow Missed In Blade Runner
3. The Spit
It's easy to miss in the rain, but the long-standing question over why Roy saves Deckard during the closing scenes have since been answered. Despite being able to simply let him fall to his death and escape with what remains of his life, the fact that Deckard spits at Roy in a final act of defiance is what ultimately saves him.
According to Ridley Scott, seeing that his adversary would rather die than beg for his life shows Roy that his "it's quite an experience to live in fear, isn't it?" question has long since been answered. He reasons that Deckard knows exactly what that life entails, so ultimately they're on the same side.