|If the glowing eyes don't make you run for your life, maybe the bloody syringe will.|
As the civil war in Rapture continued on, it was discovered that ADAM could be recycled from the blood of Splicers who had been killed in battle. In order to perform the recycling, Little Sisters were required to extract and drink the blood of Splicer corpses. It makes you wonder what is going on in the heads of the game developers at 2K Games. Anyway, the Little Sisters were brainwashed into seeing corpses as "angels," which means they have no problem jamming syringes into dead bodies to withdraw and drink their blood.
|Reduce, Reuse, Recycle|
If you decide to panic and gun down every Little Sister in sight, you are out of luck. They are immortal as long as the slug lives inside them. However, if you play through Bioshock as an evil bastard, you can "harvest" the slugs from the Little Sisters, effectively killing them, and bringing you closer to the dark ending of the game.