Special Containment Procedures: To reduce unnecessary exposure to SCP-3211, a warning message is to be placed at the start of this document. Level 4 authorisation must be required to proceed. No information regarding SCP-3211 is to be present in any resources not exclusively available to researchers assigned to SCP-3211, including the warning message.

Except in the event of an emergency necessitating knowledge of SCP-3211, no more than 3 members of the O5 council and 10% of the population of any individual Site are to have been exposed to information regarding SCP-3211 other than its existence.

SCP-3211 is to be kept in a standard non-humanoid containment chamber. Access is to be limited to tests only.

SCP-3211 exhibits a slow-acting but potent perception-altering effect. During the first 6 minutes of exposure to SCP-3211, subjects are able to observe and record SCP-3211 without issue. Once 6 minutes have passed, subjects will immediately and permanently be unable to perceive any direct information associated with SCP-3211, or observe SCP-3211 itself. This effectively quarantines information about SCP-3211 to only those who have been exposed to it for less than 6 minutes.

For the purposes of this document, subjects who have already been exposed to SCP-3211 for at least 6 minutes will be described as post-3211 and those who have been exposed to it for less than 6 minutes will be described as pre-3211.

Post-3211 subjects are consistently adamant that they are able to perfectly remember its nature despite being unable to take in new information about it. However, it quickly becomes apparent that each post-3211 subject reports a different description for SCP-3211. A selection of such descriptions, in chronological order of their being reported, is provided below.

Of note is that descriptions of the object vary only between post-3211 subjects. Observations indicate that pre-3211 subjects consistently agree on the nature of SCP-3211. However, once these subjects pass the 6-minute threshold, they will disagree on what it is. This also applies to documentation: personnel viewing this document universally report that it describes something else before it changes after 6 minutes. See Experiment Logs 3211-01 and -02 for more details.

Note that post-3211 subjects reporting unique descriptions is not universal — in several cases, the same description has been reported more than once.

The fact that those who have been exposed to SCP-3211 are able to read the list above suggests that none of those descriptions are what SCP-3211 truly is. Several theories have been suggested:

The mechanism through which SCP-3211 propagates this effect is currently unknown, though the current theory proposes that after the 6-minute threshold, SCP-3211 'injects' false memories over the original perception.

Amnestics have proven to be effective on post-3211 subjects. They will forget SCP-3211 as expected, and upon re-exposure may perceive it as something new. A method of amnesticating only the false memories has not yet been found.

► Experiment Log 3211-01

► Experiment Log 3211-02

► Document 3211-01

As an attempt to determine the true nature of SCP-3211, a collection of data has been recorded from SCP-3211 and is listed below. This data has been recorded only by pre-3211 researchers, but it is currently unknown whether the readings are accurate, or if the reader perceives them to match their current perception of SCP-3211.

Data type	Observation
Full-spectrum spectrophotometry	SCP-3211 displays absorbances and transmittances in the visible spectrum consistent with standard background reading
Mass	Mass balance placed underneath the location of SCP-3211 did not detect any weight
Hume measurement	SCP-3211 has a Hume reading consistent with baseline reality
Magnetism	SCP-3211 is not magnetic
Visual observation by D-9981	SCP-3211 is not visually present
Physical observation by D-9981	No response. D-9981 did not feel anything at SCP-3211's location
Response to basic questioning by D-9981	No response
Type-Kappa memetic sentience detector	Negative response

Incident Log 3211-C: On 2016-03-31, a researcher who was not assigned to SCP-3211, Dr. Jason Greaves, took a Class-Y mnestic¹ without authorisation and entered the containment chamber. Personnel reported being unable to perceive Dr. Greaves until his unconscious body was noted to 'spontaneously appear' several hours later. Dr. Greaves returned to full health with medical care, but did not retain any details of his encounter with SCP-3211, claiming only that he 'wasted his time in an empty cell'.

Dr. Greaves recorded a series of audio logs detailing his thought process during his encounter. However, the content of these logs propagate the infohazardous effect, and are effectively devoid of information. Their transcriptions are preserved below for posterity.

Dr. Greaves has been severely reprimanded for not following standard testing procedure.

► Audio Log of Incident 3211-F

▼ Audio Log of Incident 3211-F

Dr. Jason Greaves, SCP-3211, experiment log... one?
If you're hearing this and if, like me, you're souped-up on some heavy-ass mnestics, then you and me both know for sure that SCP-3211 does not exist. Why it's trying so hard to hide that from us, we'll never know. But, if you're not high as hell on Class Y, then in less than 6 minutes you'll only remember me just rambling on about some random thing sat in a containment chamber.
And of course, when that happens, all these logs will say is that there's nothing in the containment chamber at all.
What I'm trying to do is work out exactly what SCP-3211 is, how it works, and why it's trying so hard to hide. What does it want?
No matter what I tried and who I spoke to, I couldn't get this test authorised. But it needs to be done. So I've taken a small dose of Class Y mnestics and I'm doing this myself. I only have a couple of hours before the Class Y stops helping me remember things and starts making me forget things, so I'd better get started.

I've noticed something of a pattern emerging.
Most people who walk into 3211's cell will perceive the cell to be completely empty. Like, I can clearly see that there is nothing here.
There is nothing in the containment cell. SCP-3211 does not exist.
It seems to me like Foundation personnel — researchers and the like — will perceive the containment cell to be completely empty. People who are already familiar with nothing, who are expecting nothing, will see nothing in the containment chamber, because it is empty.
But a D-Class, for example, who is not familiar with the anomalous, will remember the containment cell being empty, just the same.
It looks like SCP-3211 does not exist at all. But I still don't understand why, if SCP-3211 does not exist, I insist on trying to prove that it does. SCP-3211 does not exist.
My head feels... foggy. I don't know if it's the SCP or the mnestics starting to wear off. I actually don't know how long Class Y lasts.

I think I've narrowed it down to three... stages. That seems to be the right word.
So, the first stage is what you see when you walk into the cell for the first time; what SCP-3211 really is. It's nothing. Obviously, as soon as my mnestics wear off, I'll forget that. And so will you. I assume you've taken mnestics.
The second stage is whatever memory SCP-3211 injects over itself when you've seen it for more than 6 minutes. Last time I saw it, I remembered seeing... my son. Who would be six. That was the second perception for me.
The third stage is that you can't perceive it at all. Its disguise is complete and it's hidden from you.
I think I know why it wants to hide. I just... need to put the words into a sentence.
It's getting hard to think. My thoughts feel like walking through ketchup.

Oh God, my head is killing me.
I'm certain it's the mnestics. Class Z literally kills you when you take it, because the effect is permanent. Class Y won't kill you... I hope? I, uh... might have majorly fucked up by doing this.
It's really weird seeing all the things you can't usually remember. There's bugs everywhere, covering every surface. The containment cell is empty. There are no bugs.
I need to sleep. I just want to sleep.

The floor is so much more comfortable than standing.
It's getting hard to breathe. I don't know if that's my lungs closing up, or if it's just the... if it's just me forgetting how. At least I haven't forgotten what it was the first time I saw it.
But I know for sure why SCP-3211 wants to disguise so avidly. It's right there, just in front of you. I'm surprised no one has seen it yet.
It's just... it's just that it's not really... it's not really there. It does not exist.

I don't know how to take mnestics, dammit. I only make them. I know how they're... how they're...
I need to sleep.
I am alone in this room. The containment cell is empty. Just... just make me forget already.
I know that it does not exist... why don't... why can't... why did you have to show him to me?
Why did you have to take him away again?
I don't think I'm going to survive.
Why hasn't anyone come to get me?

It is assumed that Dr. Greaves fell unconscious at this point. The remainder of the logs are mostly silent up to the point where a member of security staff noticed Dr. Greaves on closed-circuit monitoring several minutes later and called for help.