How can I simulate paranoia in a Call of Cthulhu One-Shot?

Question

I'm a new GM to Call of Cthulhu. I want to play a One-Shot where paranoia and hallucinations play a big role (English isn’t my first language, so sorry if some phrases are weird).

My idea is basically to play a mix of "The Thing", "The Colour Out of Space" and "The Swarm".

A strange "thing from out of space" lands on an isolated island where the players are trapped (because their boat crashed in a storm). The Thing sends out some kind of pollen or gas which makes animals and humans hallucinate. Pets and wild animals will attack, sea mammals will strand and overall, he environment will change for the worst. The number one goal for the characters is to get away from this evil island. But I want them to believe that they and/or another character is corrupted by the "evil thing".

My idea is to give them secret notes that will tell them things they saw on other characters or themselves to make them question who they can trust. I thought about maybe also "hinting" to them that they are in a "The Thing"-like setting to set them up for mistrust and simulate the paranoia. Or would the secret notes be enough?
How do I simulate hallucinations and paranoia?

Answer 1

You simulate hallucination by creating different experiences

You don't have to use secret notes, at least not for long. If you give two players, two different descriptions of what they hear, see or smell, you will create conflicting experiences. They won't know which is true and which is fake, or if both are true, or both are fake. It will create mistrust in the situation and on each other's characters.

Secret notes are fine as long as these hallucinations aren't common (yet). But soon they will start sharing the information on those notes and you might as well stop using them. When they recall information or ask you to repeat an information you gave them, cause even more confusion by saying it was something different than what you actually described, and they will hate you for this, but they are paranoid, that's the point.

Be descriptive. Even if that description is not accurate. Never give any meta information, such as game terms or exact information about what something is. For instance, don't say they sense the smell of rotten food, but look up how rotten food actually feels like and describe it indirectly ("A stale, ochre and fedit odor hits your nose, chilling your skin and revulsing your eyes. The sensation comes from every part of your body.").

In their brain, instead of thinking about their own personal experiences of what rotten food smells like, they will be focused on that sensation, trying to associate it with several different things, but not quite certain of what it is, which will leave them nervous.

You simulate paranoia by removing trust

Paranoia is slightly more complicated, but can be done using NPC's at first, make NPCs sound fishy or having second intentions, describe intense eyes or body languages that seem sketchy, like looking around before speaking, hiding something quickly when you go talk to them, whisper something in one PC's ear so the others won't listen, etc.

When they suddenly disappear once the PCs start discussing something is also a great moment for them to think "shit, we took our eyes off him for a second and he vanished to plot something, he is suspicious". Eventually, make the NPC befriend someone, and trust some information only to that PC, it will make that PC distrust the NPC and every other PC also distrust that PC. From there on, it's a spiral to a TPK, really. Either they will get their shit together, or kill each other.

Answer 2

I would recommend you provide more fluff details for certain things. If they investigate something that you took some extra time to describe and cant find anything it will make them feel paranoid. Make sure to only do this for certain things that have the theme you want them to be parranoid of. For example if you would want to have a parranoia surrounding some eldritch horror like cthulu for example describe them walking past a fish vendor and take a moment to describe the details of a still moving octopus in the window.this will have their mind of tentacles and the like. If they go to investigate further and dont find anything interesting it's all the better and will cause more paranoia. just dont over do it.