They’re found just before the fog door that leads to Gravelord Nito. You can also farm the baby skeletons in the Tomb of the Giants. You can farm 10-15 rats in the immediate vicinity before having to return to the bonfire. Having a high humanity count (up to 10) also increases your item discovery rate. If you have the Covetous Gold Serpent Ring equipped, the chance of a rat dropping Humanity is relatively high. The surrounding areas contain undead rats. One easy method to farm humanity is to warp to the bonfire in The Depths. Any fire that has been kindled provides ten flasks instead of five. Doing so allows you to spend additional humanity to kindle a fire. If you have any humanity, you can reverse your hollow status at a fire to become human.
Resting at a bonfire replenishes your healing flasks (known as Estus Flasks).
