And remember, Leto is one of the most powerful people in the universe. I do not think even the emperor can antagonize him by having his Truthsayer kill his son. Indeed, the whole premise of the first book is the emperor is worried by Atreides and concocts this scheme to kill them all. That scheme does not include a Gom Jabbar to the neck.
Nobody says the Duke will roll over and accept it. But practically, what can he do if she says he failed a test of Humanity? This is an entire society completely shaped by the fear of the non-human, for millennia.
And she is a high-up in the Imperial court. If the Duke has no power over the Judge of the Change, a local functionary, how much less over the Emperor’s literal right hand woman?
The emperor does not have complete power.
The emperor still has to deal with the Landsraad. The emperor’s Truthsayer murdering Paul would likely throw more support to the Atreides. The thing the emperor worried about the most.
Here’s the thing. The Duke has lots of power on the surface, but because he’s an honorable man, he’s in a weaker position for the underground inflighting much more common in the Great Houses. He’s by NO means unable to do it, but his strength and popularity comes from the (largely valid) perception of his honor and straightforward approach to building alliances. Not to mention the training of his troops.
The Emperor (especially if you read the prequels) is a weak, and unpopular fellow, not the least because he’s been manipulated by his advisors (especially after he temporarily exiled Fenring who was h is best and most loyal, although not entirely without ambitions of his own) and the BG. But the BG have dirt on everyone in the courts. If Paul had died, first, Jessica would likely have tried to cover it up as an accident. And because of how compromised she is, would probably have failed to do a good enough job.
Moheim would still likely have gotten out of Caladan alive, both due to the confusion, and due to her own abilities. And once she’s gone, there’s going to be minimal proof, with the entirely of the BG information manipulation to counter the Duke’s claims. And for that matter, for all his rage, would he take that step? He’s just lost his heir, his concubine, and exposed a massive weakness to his enemies. Hawat and the others would probably talk him out of it, and for that matter, the BG Chapterhouse isn’t known. So he has one target, shielded by Imperial power, and a lot of incoming threats. For that matter - it’s very likely that the other houses would consider it an internal manner - BG managing their own, especially if Jessica took responsibility for the death, rather than the act at the behest of the Emperor.
It might break him (Prequel Spoiler: the loss of a prior son, also due to betrayal, in the prequels nearly did) but if he -did- commit to vegence, the most he would likely achieve would be the death of Moheim and the dishonor of his own house. Not a good choice for an ostensibly wise Duke.
What does that mean?
I bet 99.999% of people would remove their hand from that box. This is not a test of “humanity.” It is a test to see if you are dumb enough to leave your hand in the fire because someone you never met before told you leaving it there made you human.
This isn’t coming from the Emperor personally. It’s coming from the quasi-religious Butlerian imperative. Within which framework the Emperor is given considerable leeway by the Great Convention.
Probably, and mess things up in other ways. But nevertheless, the Duke isn’t going to execute Mohiam if she claims it was justified. That would make it a form of euthanasia, not murder. “The forms must be obeyed” and all that.
Mohiam isn’t primarily concerned here about the Emperor.
You get that she could be shielded by her position in Court while still not acting in necessarily the best interests of the Emperor, right?
If Mohiam said she saw something inhuman in Paul, which would trigger a sense of revulsion in most anyone in the setting. Remember how the “Dirty Tleilaxu” are treated, for example.
99.999% of people wouldn’t be tested.
It’s a test of what the BG consider human. Which is some kind of Nietzschean ideal.
Paul is familiar with some of what the BG are and can do. He didn’t seem to think Mohiam wasn’t being perfectly, deadly, serious. Not letting yourself get killed is not “dumb”
Killing the Reverend Mother wouldn’t be a move against the Emperor, it would be a move against the Bene Gesserit themselves, and they’ve got their hooks in every Great House. Nobody would stand with the Atreides after.
This is a great point.
I just read the gom jabbar part of the book (it’s literally the first thing that happens). It’s clear that Paul has zero say in the matter:
“Paul…” Jessica took a deep breath. “…this test you’re about to receive…it’s very important to me.”
“Test?” He looked up at her.
“Remember that you’re a duke’s son.”
And when he’s with the RM:
“Put your right hand in the box,” she said.
Fear shot through Paul. He started to back away, but the old woman said, “Is this how you obey your mother?”
He looked up into the bird-bright eyes.
Slowly feeling the compulsions and unable to inhibit them, Paul put his hand in the box.
And clearly after the test, Jessica’s thoughts show she considered Paul’s death a possible outcome:
Jessica stepped into the room, closed the door and stood with her back to it. My son lives, she thought. My son lives and is … human. I knew he was…but…he lives. Now I can go on living.
Also, keeping your hand in the box isn’t sufficient to prove your humanity - the conversation between Mohaim and Paul immediately after the test:
“We Bene Gesserit sift people to find the humans.”
He lifted his right hand, willing the memory of the pain. “And that’s all there is to it - pain?”
“I observed you in pain, lad. Pain’s merely the axis of the test. You’re mother’s told you about our ways of observing. I see the signs of our teaching in you. Our test is crisis and observation.”
And I won’t quote it all, but she put the gom jabbar to his neck after his hand was in the box, but before the pain started, so the death threat occurred before he had any reason to remove his hand. It’s not like he was given an instruction sheet ahead of time - by the time he knew death was a potential outcome, he was already committed and really had no say in the matter.
I have no idea what the test would actually select for, but it’s not a unique kind of test, and I doubt that passing it would produce anything special.
The bullet ant has a sting that causes intense pain, sometimes compared to being shot or being stabbed with a red hot nail. Not only do initiates of the satere-mawe people wear gloves filled with the things, they do it multiple times.
They voluntarily bear excruciating pain multiple times, with no punishment for failure.
But its not the emperor’s scheme its the Bene Geserit’s and they absolutely would have killed Paul and shrugged and walked away (the Reverend Mother would have at least, Jessica would have been more cut up over it obviously, but would have gone along despite that). The book is pretty explicit about that IIRC, the expected result of a male taking the test was his death. And the BG would have gone back to “plan A” of trying to get an Atreides and a Harkonnen to mate to produce an heir (who would likely be the Kasssich Haderach).
Again all of that could have be klunky exposition, but instead its inferred in the Villneuve film by a single shot of a distraught Jessica barely holding it together while gaurding the door. Its a really good film.
Sounds like confirmation bias to me 
I’m sure if she was standing over his dead body she would have said “I observed a lack of observation skills and an abundance of animal qualities in him”.
“So, you were Human all along!”
“No, I’ve spent years building up an immunity to Gom Jabbar poison.” /DreadPirateMaud’dib
I did not, and do not mean to cast doubts on Villneuve and his team’s efforts to distill an incredibly language and information dense book into a watchable and enjoyable film. Far from it, I have very few complaints about his work. Just wanted to add context and textual background when countering @Whack-a-Mole’s opinions. Which, in turn, aren’t unreasonable IF you aren’t familiar with the source. The weakness of the Emperor, especially when shown the power of his troops, isn’t apparent without a great deal more information.
ETA - thank you @miller for catching my typo, which I have corrected. The prior version read “aren’t unreasonable F you” instead of “IF you”. More coffee is obviously needed today. I was trying to say that Whack wasn’t being whack, and the typo made my efforts to be responsible come out all wrong.
That escalated quickly!
FWIW:
I did read the books but that was near 40 years ago now. I did re-watch Villneuve’s movie last night with friends in preparation to see Dune 2 (sort of a refresher).
My initial claim was just a thought experiment on whether Paul could have have decided he wanted no part of this stuff and walked away. Paul had no idea what he was getting in to when he walked in that room. Paul had no knowledge or interest in becoming the Kwisatz Haderach. He certainly didn’t sign-up willingly for an excruciating pain box. It is not outside the realm of reason that he’d say he wanted no part of it. Mostly, he was obeying his mother who said he had to do what the Reverend Mother told him to do.
Having watched it again last night I think it is clear the Reverend Mother would have killed Paul. She says so. She tells Paul he could be a danger and cannot be allowed to live unless he is the right sort of person (paraphrasing). The Bene Gesserit have worked far too long to produce the Kwisatz Haderach to be stopped at that point.
Jessica was part of this plan and was supposed to have a girl (which, while not in the movie, I know was meant to breed with a Harkonnen…probably Feyd-Rautha…whose offspring was supposed to be the Kwisatz Haderach). As such, Jessica knew she could not deny the reverend mother this test. Jessica knew this was a test Paul had to pass on his own. And while Jessica loves her son dearly she has to allow this very dangerous thing to happen.
If Paul told the RM to piss off she would have killed him.
That said, I think there would have been hell to pay. Duke Leto would not have been ok with his son’s death and there would be serious consequences because of it. I bet it would get him more power in the Landsraad. Maybe he tells the emperor to piss off and never goes to Arrakis. Speculation, that would be a whole different book. But I will stand by my notion that the RM doesn’t just walk away from assassinating the Duke’s son without some major ramifications.
So not to be a dick, but I think it’s important to note that the prequels have nothing whatsoever to do with Frank Herbert, besides a genetic relationship between writers. They were written & published after his death. They’re essentially fan-fiction authorized & co-written by the person who inherited the rights to the Dune universe. So I think using them to support an argument as to what the Duke would have done doesn’t really support your position.
My personal feeling is that they’re horrible Abominations - the equivalent of a world-famous chef’s son tearing down his father’s Michelin 3-star restaurant and putting in an Applebees - but that’s neither here nor there.
Why didn’t Jessica have another baby and make it a girl? The Bene Gesserit would have the female they wanted to make babies with the Harkonnen. It seems it would solve a lot of problems.