Item #: SCP-739
Object Class: Euclid
Special Containment Procedures: SCP-739 is to be kept in a well-lit room, with its door wedged open at all times. Under no circumstances are any personnel with personality characteristics of grandiosity, psychopathy, sociopathy or solipsism to be assigned to SCP-739. If no such personnel are available, the use of mental alterations to produce such personnel is authorized.
When testing is not being conducted two D-Class personnel must be present in the room, and rotated every three hours. One is to be positioned within SCP-739 while the second stands immediately in front of the first, and is to ensure that the first D-Class does not close the door.
No testing with SCP-739 is to occur without prior approval from the project director. Any subjects that show signs of hostility after emerging from SCP-739 are to be terminated immediately.
Description: SCP-739 is a booth constructed of a lacquered oak measuring 91 cm by 91 cm at its base, 210 cm in height, and 87 cm by 91 cm at its apex. The object is in the shape of a symmetrical trapezoidal prism. The two inward leaning walls inside of the object each have a mirror affixed to them which face one another and emit a set of climbing reflections, giving the illusion of meeting overhead. The back wall and door on the booth are both featureless and unremarkable.
Any visual recordings of the interior of SCP-739 will not record the reflections of the mirrors within; all such recordings show the mirrors as a uniform black colouration, indicating a complete absence of recorded light. Faint whispers can be heard emanating from an indeterminate point within the object, however individual phrases or voices cannot be distinguished.
If a subject or item is present within SCP-739 when the door is closed, said door will be impossible to open for a varying period of time during which the booth shakes violently. After this shaking has ceased the door can be re-opened, and any objects placed subjects within will have undergone a one-dimensional, lateral inversion. All asymmetrical aspects of the subject become reversed, including internal organs and asymmetrical molecules. This change occurs on the molecular level, with L-amino acids becoming D-amino acids.
Subjects capable of communication will claim that they are unaffected, and will maintain the perspective that their surroundings are inverted instead. Exposing the subject to the anomalous effect of SCP-739 a second time will revert their lateral inversion, however some subjects still report minor discrepancies in their environment afterwards. When questioned, subjects will be unable to identify any specific discrepancies, attributing it to an instinctive feeling.
After being affected by SCP-739 several times, subjects will begin to display prominent physical and mental divergence from prior to testing. Physical characteristics that are considered undesirable to the test subject1 will gradually diminish until absent or replaced by favourable characteristics. Altered subjects are unaware of these changes and are insistent that no changes have occurred.
Affected subjects will also progressively develop divergent memories of their history prior to exposure to SCP-739. These memories will become more prominent with each time the subject utilises SCP-739, eventually resulting in a history that the subject would consider more favourable than their true history, however universally result in the subject being inducted into the Foundation's D-Class regimen for testing with SCP-739. Subjects will lose familiarity with individuals who become increasingly absent in these false memories, and will claim familiarity with individuals that they had never encountered - in most cases these individuals are purely fictitious, or are portrayed in a stereotyped manner.
If the door of SCP-739 is closed without any objects or subjects present within, the item will initially function as though such was present. After unsealing, an entity of unknown physical appearance will emerge from SCP-739. These entities uniformly appear as a featureless, dark blur on any visual recordings they are present on, and are cognitohazardous to observe in person. Personnel questioned prior to amnestization will state the entity is foreign or unknowable, frequently referring to it as something that doesn't exist. All such entities that have emerged from SCP-739 to date have utilised shockwave pulses in order to damage their immediate environment and injure or kill nearby personnel (see Experiment 739-23).
Following the initiation of D-Class testing, SCP-739 will no longer recognise the presence of inanimate objects placed within when closed, functioning as though its interior was left empty.
Addendum 1: Interview Log

Interviewed: D-53682
Interviewer: Researcher ███
Foreword: D-53682 had been altered by SCP-739 multiple times in succession before the interview was conducted. Prior to the initiation of these experiments, D-53682 was a Caucasian male 154 cm in height, weighed 65 kilograms and had lost their left arm below the shoulder from an amputation. Following the conclusion of these tests and during this interview, D-53682 was a Caucasian male 203 cm in height, weighed 105 kilograms and had regenerated their lost arm.
<Begin Log>
Researcher ███: Please state your full name, followed by your designation.
D-53682: John Kate Ball, D-53682.
Researcher ███: Are you sure that is your name?
D-53682: What do you mean, 'am I sure'? It's my name, I've had it since birth.
Researcher ███: Our records say that you - D-53682 - are named Jesse Klarent Ball. Before testing began, you told us that was your name.
D-53682: No, my name is John Kate Ball. It's always been John Kate Ball, like I said before. Someone must be messing with your systems, you should get Cam to see if he can fix it.
Researcher ███: Cam?
D-53682: Yeah, Cameron. You know, the big tech expert here? Practically fueled by nacho chips?
Researcher ███: When did you meet Cameron?
D-53682: Man, its been so long ago…I think we met in the cafeteria at Site-83. No, wait, we met in school, didn't we? Ah, well, it doesn't matter.
Researcher ███: Can you tell me why you were incarcerated?
D-53682: Fraud and money laundering. Let me guess, I'm wrong again?
Researcher ███: Yes. You were guilty of two counts of second degree murder.
D-53682: Yeah, I'm fairly sure I'd remember killing someone, and I'd appreciate if you didn't suggest I had.
Researcher ███: Very well. Do you recall what happened inside SCP-739 when the door was closed?
D-53682: The booth thing, right? I uhh… I sort of remember something foggy, before the door opened up again.
Researcher ███: Continue.
D-53682: I was alone when I went in, right? I remember hearing voices when I stepped in. I think… I don't think those things belong…
Researcher ███: What things?
D-53682: I'm not really sure, just… Well, I suppose you could always go see for yourself. I think they'd be happy to see you.
<End Log>
Closing Statement: Attempts to communicate with D-53682 and gather more information about SCP-739 and the changes the subject underwent are currently ongoing but due to the subject's unwillingness to cooperate, the information gathered thus far has proven to be inconclusive. Any personnel cycled through SCP-739 are to be interviewed immediately unless they pose a direct threat to Foundation personnel, at which time traditional means of termination are authorized to be used at the discretion of the project director.

Addendum 2: Incident Log

Experiment 739-23
Date: ██/██/████
Procedure: SCP-739 was closed and opened without any items or subjects being present within.
Results: An entity of unknown origin emerged from SCP-739 once the standard ten-second sealing state had concluded. The physical appearance of this entity (retrocausally designated SCP-███-1-D) was concealed on all visual recordings of it, appearing as a darkened region on such. Personnel present in the testing chamber at the time displayed extreme discomfort at the appearance of the entity and attempted to avoid observation of it. SCP-███-1-D showed an immediate awareness of Site-83's2 layout. The entity closed SCP-739 behind it, triggering a second sealing state.
SCP-███-1-D proceeded to breach containment by use of directed shockwave pulses in excess of 210 decibels to destroy impeding barriers and kill any personnel it encountered, primarily armed first-response containment teams. The entity displayed a focus on eliminating as many personnel as it was capable of, showing no acknowledgement of other objects or entities unless such impeded or attacked the entity to some capacity. Containment efforts were severely impeded due to the visually cognitohazardous appearance of SCP-███-1-D.
After ten minutes SCP-███-1-D collapsed. An automated autopsy of the entity revealed that it was not suited to terran environments, and succumbed to an approximate analogue of oxygen intoxication. It had suffered non-lethal injuries during its containment breach, apparently being capable of rapid regeneration while active.
During the containment breach of SCP-███-1-D a second similar entity, designated SCP-███-2, emerged from SCP-739 and immediately proceeded to escape from the perimeter of Site-83. It is unknown if SCP-███-2 is more adapted to terran environments than SCP-███-1-D, as the entity has not been observed since its initial breach.

Addendum 3:
Analysis of the auditory pulses utilised by SCP-███-1-D to attack personnel have been discovered to be heavily distorted humanoid speech. Below is a transcript of several phrases stated by SCP-███-1-D.

You let me in!

There is so much to do.

We will enforce what your messengers taught us.

We are ready to complete our work.

Why do you ignore me?

Will you look if we all scream together?

We will earn your acknowledgement.

Footnotes
1. Typically features such as facial scarring, prominent acne, disfigured or absent limbs, excessive weight and/or insufficient or over-sufficient height.
2. The site SCP-739 was present at during Experiment 739-23.

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