In this paper John Bonnel argues that the representation of the serpent in Eden as having a human head was common to drama and iconography; that it is first noticeable in the thirteenth, or the early part of the fourteenth century, being then a startling innovation in art; and that in all probability it was the mystery play which, to facilitate the dialogue between Eve and the serpent, first adopted it, from a literary source. This argument adds drama to the spectrum of plastic art and literature that normally operates alone in discussions of this kind, unifying these three arts to produce an explanation of a sudden change in the normally stable iconography of Christian art. This piece is useful both for its expressed thesis and to show how live art can affect other forms.