Mandrakes or Mandragora are human like plants that scream when pulled out of the ground. Like the banshee, their scream is fatal to whoever hears it. Hence dogs are used to uproot them. Mandrakes flourish near old gallows, the aura of dying criminals promotes the grownth of these plants. Young mandrakes can't kill with their screams yet, they can only knock people out for a while. Hogwarts grows young mandrakes to create a cure for petrification. However mandrakes are also used to create a sleeping potion so powerful it is referred to as the draught of living death.