According to the museum website:
‘It seems clear that Howison was showing serious signs of mental illness before his crime. According to Simpson, he was a “solitary, silent, wandering individual”, frequenting only the company of a cat and child. He had become miserably superstitious, fearing supernatural enemies, and had resorted to ceremonies to protect himself such as salting his bed and head, wearing a bible around his neck or wrist and habitually wounded himself by pricking both his hands and feet. He was afflicted by hallucinations, often sitting brushing away flies off his hands for hours where no such could be found. It would seem that Howison had undergone a rapid and profound change of personality.
Source: Anatomical Museum website, University of Edinburgh