The Boys of Silence are BioShock Infinite bad guys. The original plan was for them to make you pay for all your noise.
The Boys were going to wait to attack the player, BioShock Infinite's art director Nate Wells explained today during a panel about the game's bad guys at the PAX East convention. They were going to wait for you to make too much noise. The bullets you fire? They'd hear them and sort of collect their sound. The steps you take? They might collect those too. Eventually they'd have enough and attack. These enemies would compel you to choose quieter weapons, the game's creative director, Ken Levine, added.
Unfortunately, the Boys won't do that. Well, maybe it's fortunate, because the Irrational guys said the concept didn't work. Players wouldn't understand what was happening. They'd not see a Boy of Silence who was collecting their sound and wouldn't understand why one was suddenly attacking them.
The Irrational team tried to compensate by having ambient noises drop from the game's environment as a Boy of Silence collected sound. That wasn't the right fix. So the function of the Boys of Silence has changed. We'll find out their new set of rules when BioShock Infinite is released this October.