In Scene 9, Robin and Rafe have been using Doctor Faustus's book to do some conjuring and Robin holds up the proof of their success: a stolen silver goblet
In Scene 9, as Robin holds up their success, a vintner (wine merchant) approaches, demanding payment for the goblet
In Scene 9, Robin and Rafe deny having the goblet to the vintner and secretly pass it back and forth while the vintner searches each of them
In Scene 9, after the vintner asks for the Goblet back, Robin insists on searching the vintner, uttering an incantation while he does so which summons Mephastophilis
In Scene 9, after Mephastophilis appears in front of Robin and Rafe, he turns Robin into an ape and Rafe into a dog