Sacrificing two Damsels (living or dead) is the fastest and safest way of earning 16 favor. Due to the great increase in survivability granted by the Kapala, it is usually worth missing out on a kiss or two in order to gain enough favor quickly. It's a good policy to sacrifice any Damsel that appears on a level with an Altar if you don't yet have the Kapala, unless you're attempting to unlock the Changing Room, or have extremely low HP and there aren't enough substitute enemies in the vicinity to make up for it.