If the script of Ladies of the Big House seems a bit more authentic than usual, it may be because it was written by an actual prison convict named Ernest Booth. (rottentomatoes.com)
The actions of the guards and the reactions of the prisoners were something that Zimbardo didn't predict, as the basement rapidly took on the appearance & mood of an actual prison, and the volunteers began to turn into their roles, even knowing that this was all make believe. (dvdtalk.com)