"Deck the hall with boughs of black hellebore" hardly has a festive ring, but Robert Bentley's Medicinal Plants assures us that this plant that blooms in the bleak midwinter is commonly known as the Christmas Rose. Bentley reports that black hellebore has a slightly bitter taste and causes a tingling sensation on the tongue. In moderate doses, the plant was used to treat mania, melancholia, and epilepsy. It was also used as a medicine for domestic animals. In large amounts, though, it is poisonous. At Hogwarts, the plant's calming properties are utilized in Professor Snape's Potions class to make the Draught of Peace, but best to keep in mind Bentley's description and skip it at the Yule Ball.