No need for correction.If I am wrong, I am sure WS will have no problem correcting me.
A "snatch block" can be used in a dead-head set up... "snatch block" refers to a pulley that opens in some way to facilitate quick threading of the rope, cable, or whatever.
A "dead-head pulley" (snatch block or other) is attached to a non-movable anchor point (the dead-head) allowing a direction change. The biggest advantage is it allows a short rope/cable to pull a tall tree because it puts you out of the way of the fall.... and, if you're using a vehicle, it doesn't lift "up" on it and remove traction. I normally use a length of chain from the dead-head to the pulley... 99 times out of 100 the tree will fall directly on the pulley.