Demon Item Mover
Shift-right-clicking a wooden log with a Demon creates a demon item mover. The side you right-click on (it can't be the top or bottom) is the input side, and the opposite side is the output side.
Demons can access chests, chest minecarts, and furnaces. They can't put fuel into furnaces, but who needs fuel when you have demon slaves?
Angry demons have extra abilities:
Tier 0 (0% - 33% anger): The demon will only move items from one inventory to another - no special abilities.
Tier 1 (33% - 67% anger): If there's no input block (including a minecart track), the demon will break the block in front of it. If there's no output block, it will throw items on the ground.
Tier 1 (67% - 100% anger): If there's no input block (including a minecart track), the demon will break a 3x3x3 area of blocks in front of it. If there's no output block, it will throw items on the ground, unless they are blocks, in which case it will throw blocks on the ground. This can be used as an automatic block placer! It can also be used to trigger a Demon Altar after you already picked up the Congealed Blood.
Usually the demon item mover will hold a minecart in place until it's done, but if a demon cart throws a block out of a minecart, it will only take one block. This is handy for re-planting saplings in a tree farm.
If a chest is placed on top of the demon item mover, it will only move items which match the ones in the chest. This even works with angry demons. Apparently the laws of magic somehow prevent them from smashing your chest in a fit of rage.