 Unlike in the previous game, Little Sisters will not run away from the player when they meet, but instead greet them, able to be "Adopted" to collect ADAM or "Harvested" on the spot to collect greater amounts of ADAM at the cost of their lives.In the downloadable content for "BioShock 2" called "Minerva's Den", the player takes on the role of Subject Sigma, previously known as "Charles Milton Porter", on a mission to recover the Thinker from Reed Wahl, Porter's former partner that betrayed him to Andrew Ryan and leading to his transformation into Subject Sigma.The Thinker uses Porter's likeness to guide the way for Sigma, and at the end of the storyline, Sigma is returned to his original form as Porter.