RALPH: Hebona, or hebenon, as it appears in some versions of the play, is a poisonous plant. It's actually not certain which plant the term refers to — it's possible that Shakespeare was referring to henbane, a poisonous bush, but it's also possible that the term was supposed to refer to the yew tree, the most toxic tree in Britain, which was easily observed by the fatal consequences when cattle or horses ate its foliage. The yew tree is also traditionally a symbol of sadness.

SARAH: If it is indeed the yew tree that Shakespeare was referring to, he may have been indulging in a little botanical word play when he describes how the symptoms of the poison "barked about" his smooth skin, as if the poison created a kind of tree bark on the skin of the King.