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?
So why did 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.
Like Spooner says the building design of USR is "messed up", 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 a 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.
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.