Mandrake, also known as mandragora officinarum, has a long tap-root that resembles a human form. This resemblance created the superstition that it literally shrieked when it was uprooted. Those who heard the scream were to die, or, if it didn't kill them, it caused them to go insane.
This relative of the potato family was a popular anaesthetic during the Middle Ages. In the Elizabethan Age it was used as a narcotic.