The Saw that i'm going to refer to is the two maned kind, or the lumberjack saw. It usually took two people and a large saw to cut through the persons skin, bone, and organs. When a person was sawed open like the picture above, they usually died by the time it hit their naval or even their breasts.
The picture above shows the use of the saw in Fance, where it was used on pregnant woman who held "the children of the devil".