d647950c_d___Game_Guide_and_Walkthrough__BONE_CHARM_PROPERTY
[BONE CHARM NAME] Rat Scent [USEFULNESS] The charm may turn out to be useful regardless of the preferred style of game play, although rats can be avoided easily, on the other hand, or simply killed. [BONE CHARM PROPERTY] 
Rats attack Corvo only if he comes really close.
Bone Charms - list - Collectibles - Dishonored - Game Guide and Walkthrough
BONE CHARM PROPERTY