This transformation is brought about, not by experimentation with chemicals as in Stevenson's original, but through the supernatural agency of a bust of Janus (the Roman god of the doorway), which Warren / O'Connor purchases in the opening sequence as a gift for his sweetheart, Jane Lanyon (Margarete Schlegel).
Janus | head | head of state | Beavis and Butt-head | Alec Head | Murray Head | Head Start | Anthony Head | Head Start Program | Diamond Head | Janus (mythology) | Human head | Head teacher | Machine Head (band) | Machine Head | Head Over Heels | Head of the River Race | Eddie the Head | Hilton Head Island, South Carolina | Edith Head | Diamond Head (band) | Beachy Head | The Bodley Head | Lizard Head | Head & Shoulders | Head over Heels (Paula Abdul album) | Head over Heels | Diamond Head, Hawaii | Women's Head of the River Race | Turk's head knot |