SCP-4031 is titled The Amnesiac Redemption. What is an "amnesiac"? An amnesiac is a person with amnesia. In the early days of the SCP Wiki, the fictional drugs that make people forget things were known as amnesiacs. It didn't take long for the standard consensus of this to turn on its head, allowing the Wiki to adopt the word "amnestic" (a more correct term) in place of "amnesiac".
This article is based on that semantic confusion.
What is SCP-4031? SCP-4031 is an amnesiac: a person with amnesia. This person has the properties of an amnestic: any subject in sensory or memetic range becomes confused, forgetful, and gets a bad taste in their mouth. This amnesiac also acts like an amnestic: their amnestic properties are fast-acting. And because you become forgetful when you're in range, researchers were woefully unable to determine any physical or quantitative properties beyond the fact that it acts like an amnestic.
The article is intentionally masked with confusion. From the perspective of the reader (a fellow researcher, presumably), it looks like the research team was unable to mount any proper efforts toward investigating the anomaly. The threat level is undetermined, there are no containment procedures, and the description is a few sentences long. The average reader won't immediately get that this is an amnesiac and not a proper amnestic — the words are close enough in spelling. And if it quacks like an amnestic, and walks like an amnestic…
The only thing that might make the unsuspecting reader think something is off is the fact that the amnesiac makes male vocalizations. Amnestics don't typically do that, do they?
Glossing over the fun of the experimentation log (it's based on the conceit that subjects — not necessarily people, but test subjects — become forgotten when they make contact with the amnestic amnesiac), we get to the addenda. Researchers consume mnestics: drugs that make you remember.
And the veil over this anomaly is lifted: it was a guy with memory loss causing all this confusion. How did he get memory loss? "Subject possessed significant cranial damage". But what else do they find? "Subject possessed lacerations, emaciation, a broken left clavicle, and blood loss in the oral cavity." Over the course of experimenting with this guy (note that there's no passage of time here — testing could have occurred across three hours, three days, or three weeks), they gravely injured him. And because he's an amnesia patient that makes other people forget about him, he couldn't stop the testing, and the researchers could never figure out what horrible things they were doing.