CHAPTER ONE: Two siblings, one brain
We used to have brother and sister come in once in a while. They were early-to-mid twenties and apparently lived together. They had a weird incest vibe about them and their distorted facial features gave the impression of inbreeding. That isn't the weird part.
The strange thing is, they both occasionally behaved as if they had mild to mid-level retardation, but not always After they had been in a few times I began to notice a pattern. When the sister would bring the computer up to the counter, she would act fairly normal, talk about her job and describe her computer problems. The brother would hang back like he was a mute and stare at the wall and pick his nose. BUT when the brother would bring the computer to the counter, he would speak normally and be coherrent and the sister would hang back and speak in baby talk with half open eyes.
It's been a few years since I saw them last, but never have I seen them both be intelligent at one time, and never have I seen them both act disabled simultaneously. My theory is they somehow had a psychic link and shared their intelligence between each other, about 150 IQ points. Sometimes the brother would have an IQ of 100 and the sister an IQ of 50. Sometimes vice versa.