User blog comment:Evans0305/Cult of Rapture: The Secrets of Minerva's Den/@comment-24.217.232.167-20100915023342/24.217.232.167-20100915122616/Willbachbakal-20100915163722/24.217.232.167-20100915204838/Willbachbakal-20100915210206/Willbachbakal-20100915210856

Correction: It didn't even get mentioned in-game, it was Steve Gaynor who casually said in an interview that the biomass was the origin of the slug's mutation.