That severed hand is called a "Hand of Glory" in occult circles.
The mandrake is a plant that allegedly grows only on the graves of executed persons.
In reality, it is the nightshade plant and grows well in dry soil. Josephus discusses it in his Antiquities.
The "hand of glory" is supposed top have all kinds of properties, including the ability to render someone motionless or to open locked doors.
This is hardcore occultism.