; Date: February 25, 2020
It is established lore in Doctor Who that Cybermen are people - humans - that put themselves into machine suits. To live in the machine suits, the Cybermen suppressed all emotions, lived only on logic, and to implement that decision they installed Neural Inhibitors that turned off normal emotional responses. But in this set of stories we're seeing a Cyberman, called The Last Cyberman, whose neural inhibitors are turned off, and that does not result in his death. Therefore we're seeing a whole new kind of twist to the Cyberman story.
One of the more successful methods The Doctor has used against Cybermen is to disable the neural inhibitors. In every case, without the neural inhibitors the human person inside the Cyberman suit starts screaming and basically explodes. In other words, the human cannot take what has happened to them that they are inside the Cyberman suit, and the emotional turmoil causes their death.
By the way - Cybermen are obviously symbolic of extreme interaction with machines.
In any case, that's one of the answers above - Cybermen scream when their neural inhibitor is turned off.
In The Ascension of the Cybermen - the story is that a human, The Last Cyberman, willingly chose to become a Cyberman. He, apparently, was in full support of the Cyberman cause. But - it seems that the machine that was to do the Cyberman conversion refused to finish the job, and so he was only wearing a half Cyberman suit. Further, the neural inhibitor was not working, and unlike all other Cybermen we've seen The Last Cyberman is full of anger and gloats and grandeur, meaning that he has a full set of emotional responses.
Somehow, for him, being in the Cyberman suit with non-functioning neural inhibitors is not causing him to scream.
In The Haunting of Villa Diodoti, we saw The Last Cyberman become infused with The Cyberium. This is some kind of mutual consciousness thing of the Cyber race. Therefore, The Cyberium chose this dude to be the savior of Cybermen, and to reawaken the Cyber race.
That's the context within which we see The Last Cyberman board this Cyberman Troop Carrier, and begin the process of waking up the Cyberman army on-board.
He describes this as The Ascension of The Cybermen, so this is seemingly unlike all other cases where we've seen a Cyberman army waking up.
In Cyberman culture we've seen on multiple occasions that they'll keep a bunch of Cyberdudes in cold storage suspended animation. Then when they're needed, the Cyberdudes will be awakened, ready to go to do whatever task is required. This goes back to the Second Doctor story, The Tomb of the Cybermen, on the planet Telos, where a group of stupid humans who desire to live by logic seek to wake up some Cybermen.
In every such case the Cybermen simply wake up - no screaming.
In this case, the Cybermen are awakened, then The Last Cyberman uses this gun-thing on them, and they start screaming.
Given all this - it's clear that The Last Cyberman is doing two things for each awakened Cyberman:
- Turning off the neural inhibitor
- Teaching them how to ride their emotional wave without screaming