Contains spoilers for A.X.E: Death To The Mutants #1!
Marvel superheroes quite famously never kill their enemies, but during the Eternals vs X-Men war, one hero goes out of his way to not kill his enemies - thus leading to the single most ridiculous non-lethal weapon ever used in comics. The war between the two groups is unique in Marvel history, as neither mutant nor Eternal can technically die while either side has methods of resurrection available. Now in A.X.E: Death To The Mutants #1, one Eternal uses a creative weapon to make sure he never takes a life again - and for good reason.
When Druig insists that the mutants represent "excess deviation" and thus are in violation of the third Eternal's principle, the Eternals declare war on the X-Men and Krakoa. Druig is especially concerned about the X-Men's ability to return from the dead, thanks to five mutants (known simply as The Five) and their adherence to the resurrection protocols. Of course, the Eternals can resurrect too, leading to an interesting war in the Judgement Day event in which no combatant can ever truly die - and alas, the price of fighting is passed down to the humans of Earth instead.
In A.X.E: Death To The Eternals #1, written by Keiron Gillen with art by Guiu Vilanova, Ikaris and a team of Eternals (rebelling against the other Eternals and Druig) make their way to the heart of the Machine: Olympia, buried deep inside the Earth. Zuras stands in Ikaris' way, but the Eternals leader uses a specialized device that. "temporarily teleports a small part of Zuras' brain into another dimension, leaving his mind with a missing connector." Zuras is taken out of the fight, since he cannot think - but since the missing piece of his brain is only temporarily removed, he doesn't die either. It is vitally important that Ikaris refrain from killing Eternals, for every Eternal temporarily killed is a human permanently killed in their place.
The Eternals' greatest and most tragic secret is the fact that the Machine uses human life force to resurrect Eternals. Thus, Ikaris' instructions to Jean Grey include "Kill no Eternals" (though he doesn't mention why). Even so, the weapon used against Zuras is innately ridiculous, and looks for all the world like a simple firearm that kills Zuras outright. Fortunately for him (and for any humans who would have been chosen) Zuras is only temporarily rendered unconscious.
The vast majority of Marvel heroes never kill, and the few exceptions were situational (Captain America in World War II, Hawkeye killing the Hulk under Bruce Banner's orders). That being said, the lengths that said heroes will go to not kill borders on ridiculous. The Eternals may never be able to die, but the humans can - which makes Ikaris' unique weapon test the audience's suspension of disbelief, but makes sense from a narrative perspective.