Because I have some time on my hands, as well as it having been soooo fun to think up, I’ll explain here about the “gas embolism” I threatened Nysa with earlier.
As I said in the char file, the Tyrant is pretty meh when it comes to telekinesis, but it knows how to use what little it has to great effect, and everything (short of psionics) checks out in real-world physics.
What happens is that it creates a psionic force field in a blood vessel in the brain, a mere fraction of a millimeter, and pushes fluid away. This creates a low pressure area that is filled up by the nitrogen always dissolved in the blood, much like with decompression sickness in divers. There is now a bubble of gas in a capillary in the brain. It lodges itself in the blood vessel, cutting off blood flow to the area, starving brain cells of food and oxygen, rendering them inoperable and soon killing them. If this happens in the respiratory center you lose all control of your lungs. You stop breathing, suffocated to death by a bubble of air. Fun, right?
But there’s more! If somehow you do get put on an artificial respirator in the middle of a ‘nid attack, you now have a dead lump of tissue in an inoperable part of the very core of your brain. The cells will decay and fall apart, poisoning the blood with bits of dead cell. The area may also become a breeding ground for germs and become infected. Even if septicemia doesn’t kick in, you have all chances of ending up with an autoimmune condition in you brain, your own immune system ripping apart anything it sees, friend or foe, to contain the threat.
Have a nice day!
The justification of not spamming this insta-kill button is that you need to be within spitting distance (from a human PoV) to the Tyrant itself. It needs vast amounts of its attention span to follow electric impulses from lungs back to their source in the brain in whatever species it’s up against, single out individual blood vessels in the hectic mess that is brain tissue, then make the bubble. That attention span is generally taken up by micro-managing a million-strong army of chittering bugs. Furthermore, it can’t pass that amount of attention through the infinitely more psychic Zoanthrope brain-bugs.
So this will likely happen when something extremely stupid and horribly annoying takes on an extremely bored Tyrant in a fist fight. Low likelihood in Warhammer 40k, not so much here.