Also, if the player chooses to adopt the Little Sisters rather than harvest them, then the player will need to get ADAM by protecting the Little Sisters when they get ADAM from dead Splicers. However, the player can take the time to get resources and set up traps because the player can choose the time when the Little Sister gets ADAM. After the player rescues all the little sisters in a level, the player will then fight a Big Sister, a Little Sister who grew into an adult. Big Sisters are difficult to kill because they have a lot of health, they can kill the player quickly, and they can use plasmids to fight the player. However, the player will get a lot of ADAM if they kill the Big Sister.