Twisted Mentats were Mentats who originated from the planet Tleilax. They were different from normal Mentats in those characteristics nonessential to pure computational ability. These variations took the form of body structure, emotional nature, and psychological make-up, depending upon customers' orders. Mentats produced by legitimate schools were also bred with certain characteristics in mind, but these were relatively benign in comparison to the Tleilaxu machinations and not the result of genetic engineering.