One way to prove whether or not Stephen Byerley was a robot would be to put a loaded gun in front of him and order him to shoot himself. If he is human, then he can refuse. If he is a robot, then he will be compelled to obey.
Based on what we see of him, I suspect Byerley would shoot himself anyway, human or not. If he could get away with shooting himself somewhere non-lethal, he would, and then refuse to let anybody examine the wound. The only way to be really sure would be to explicitly specify a lethal injury — and killing him is further than most people would be prepared to go to settle the question. — Paul A
So you order him to shoot himself. Has someone else ordered him to do otherwise, to stay safe from harm? As a tiebreaker, does Byerley know he'll keep doing his best to protect people so long as he exists, such that shooting himself at this point will only result in more harm to humans?
Del Spooner is played by Will Smith, a black man. Spooner's "canner" slur that he uses towards robots harks back to, ugly as it is to think about, the way racists use the word "nigger" for black people. Perhaps done intentionally, to show that Spooner is so blinded by bigotry that he doesn't even see the possible connection and that he's doing to robots what was also done to black people generations ago.
A somewhat dark interpretation of this is that, while everyone else sees robots as slaves, Del is enraged by the thought of having to respect them as normal. He's become the "classic" bigot who resents diversity (in this case, humans and robots living together) while the rest of the world is the "modern" bigot who are fine with it, as long as they stay in their place. Which makes sense, seeing as Del is characterized as being into retro things.
So why didn't the robot running with the bag stop when Spooner ordered it to? This would appear to violate the second law, except that the owner's inhaler was in the bag. Stopping as instructed might violate the first law by allowing the robot's owner to come to harm.
He may not have known that Spooner was talking to him. It was a crowded street; he could have been calling after anyone. Indeed, the robot had no reason to think that someone would be telling him to stop.
Like Spooner says, the USR superstructure has "poor building planning," with thin walkways and no hand rails leading to the main console controlling VIKI's interface. When you think about it, really, who's going to try and shut off a super-computer suspended far above the ground floor on tiny metal pathways?
Every day Del's grandmother makes him one or more pies, which he eats in one sitting. It seems like an arbitrary character trait, but if you think about it all the sugar and calories probably power his artificial arm. Also explains him dumping a half-dozen spoonfuls of sugar in his coffee toward the beginning. (Unless that's a pun on his name.)
As well as the seemingly gratuitous shower scene early in the film, which serves as a point on second viewing.
When asked about Lanning, Sonny says he "did not murder him!" Lanning ordered him to. It was an assisted suicide.
Dr Lanning is shown to have planned his Batman Gambit insanely well... anticipating Spooner and Sonny's actions throughout the story. Given his closeness to Calvin, he no doubt anticipated that when Sonny attempted to run, she'd naturally seal the room. Sonny would then naturally follow in his footsteps by throwing himself out of the window and landing exactly where his body did.
Lanning also may have intended this so that he would land in front of the 3 Laws, symbolising the creator's wish for the death of the 3 laws. When Sonny would do this the force of him landing beside the 3 Laws, would send cracks running towards them, symbolising that Sonny, the creation, would break them.
Why did Lanning know that a second Positronic brain would allow a robot to outright defy or reinterpret the 3 laws? Simple! He had done it before. VIKI! Viki had in fact been the basis! It's why she could effortlessly tell the other NS-5s to disobey the rules! And how did she start "reinterpret" the rules? The first NS-5 that was hooked up to her wireless signal. She had already been given another brain, and so on and so forth. It's why Lanning created Sonny and gave him no wireless signal, Sonny wouldn't be able to defy her had he been on a wireless signal like his "Brothers" because 2 Brains are trumped by thousands!
Sonny's second Positronic brain, the one that lets him override the Three Laws, is built into his chest. Dr. Lanning gave him a heart. No wonder VIKI doesn't understand, and Sonny does, that her plan is "heartless."
Why are robots designed to be personal assistants and servants super fast and super strong? They are also designed to protect humans, and are thus overengineered to be capable of, say, quickly extracting a struggling powerfully built man from a wrecked car.
Which in itself would be a massive marketing boon, but also: "It can change the engine in your car!" (Show an NS-5 lifting the engine block out by hand.) "It can do landscaping!" (Show an NS-5 ripping a tree stump out of the ground by hand.) "It can even make your children smile!" (Show an NS-5 leaping thirty feet into the air to retrieve a child's lost balloon.) "Order yours today!"
Because "Protect Humans" is one of the Three Laws? As shown with the old models, they can save people's lives by rescuing them with super strength and/or retrieving medicine with super-speed. The Three Laws extend to all humans, not just the owners.
They're machines. They're very heavy. (Look what happens to the floor when Sonny lands in the USR lobby.) They probably have to be that strong just to move around.
When the NS-5s turn up at the junkyard, the other robots burst out of their containers to fight them so Spooner can escape. Dr. Lanning's narration lampshades how this could be seen as them simply responding to their programing in interesting ways (though that raises the question of how they knew the NS-5s were a danger to Spooner), or if they were demonstrating true intelligence while also obeying the Three Laws by reacting as one group to fight the NS-5s together.
Related to the above: The NS-5s are able to defeat the older robots not only because they are stronger, but also because their networking allows them to coordinate their efforts more easily.
With the whole world in her pocket thanks to the NS 5's. It seems illogical for VIKI to have killed Robertson. Until you realize the man must have been persistently trying to shut VIKI down once he learned the truth. When he continually refused her benevolent dictatorship, he signed his own death warrant. Though on the plus side, it shows the man wasn't one hundred percent a dick like Spooner thought.
When Spooner is being attacked in his car by the robots who nonsensically insist he's having a car accident? That's not just VIKI employing Implausible Deniability. The robots are hallucinating that they're saving him, to get around their first law restrictions. Think about that from their perspective now. It's unpleasant.
Especially considering how all the NS-5s were locked away at the end of the movie for their part in the rebellion, when they were literally on remote control the entire time. If robot's have any sort of self-awareness, they have to be wondering why they're held accountable for VIKI's actions.
Not to mention what the overall social backlash is going to be like for the other robots that had nothing to do with it, remote controlled or otherwise. Consider that the older robots in the junkyard had at least the awareness to realize that the supposedly Three-Laws Compliant NS-5s were a very serious danger to Spooner.
Spooner's grandma Gigi "conveniently" wins an NS-5 in a raffle just before the robot uprising kicks in. Was it luck, or was VIKI setting up an I Have You Wife situation where Gigi would be held hostage to force Dell to stop his attempts to resist her takeover.
After everything that happened, robot phobia and racism will likely rise.
The very things Robertson was trying to prevent.
Was anyone planning to empty Lanning's house of his belongings before the demolition the next morning? Had Spooner not gone snooping around there, the demolition bot would have inadvertently killed Lanning's cat!
Very carefully piggybacking off of two above interpretations: While the one super-wealthy character we see is white, and many of the African American ones are working-class, more overt forms of racism seem to be moot. A very depressing interpretation of this could be that all of the menial labor being given to robots fulfills the human construct of classism by making the lower class literal objects rather than people of color who are forced into lower-class living by those in power. After all, nobody sees the robots as human enough to kill, why should they be human enough to question enslavement? And while Spooner's technophobia is justified, it's not like anyone who disbelieves him actually respects robots as anything more than literal commodities. John even refers to Sonny as "a can opener," not too far off from Del's "canner" slur. Operating from a relatively limited perspective one might fear that VIKI's actions are going to result in some considerable backlash against personal robots, forcing humans back into those menial jobs and re-igniting systemic oppression.
Has anyone been taking care of Dr. Lanning's cat since he passed away? Given the setting, it's entirely reasonable that there's a USR product that does exactly that, but the first we see of the cat is when it's hanging the house that's due to be demolished the next day.
Blink and you'll miss it, but Spooner gave the cat to his grandmother.