Originally posted by Faceplant8:

Listen for flies. If you hear flies on the other side of the mud pile, that means the room you're about to enter contains a body pile.

Gold.

Also, if you need to farm wraiths for chains for some reason but you are afraid to stay for the night, approach from a neighboring friendly biome and scout the swamp. Wraiths float and are easily spotted in the gloomy ambiance. Wait for them to get closer, use a ranged attack whilst sneaking to bring them down to half HP, finish them off when they get to you. They are perfectly survivable, unless they've got company. Make it quick so as not to attract much attention -- easy chains to collect and store for later use.