I thought it was a person but
Arnold-Chiari malformation is a malformation of the brain. It consists of a downward displacement of the cerebellar tonsils and the medulla[1] through the foramen magnum, sometimes causing hydrocephalus as a result of obstruction of cerebrospinal fluid (CSF) outflow [2]. The cerebrospinal fluid outflow is caused by phase difference in outflow and influx of blood in the vasculature of the brain.
That's according to wiki....
TPBM is surprised and thought it was a person too.