'Lord' quoth he! That a monster should be such a natural!
These words come from Trinculo, who communicates shock that an animal like Caliban should utilize a term of regard like "Master." In saying that Caliban is "a natural," Trinculo makes a quip on the possibility that beasts are unnatural, yet he likewise suggests that Caliban is an imbecile—that is, "natural" instead of refined. Maybe more than Caliban's appearance alone, the disjuncture between his discourse and his appearance strikes Trinculo as monstrous. Critically, Prospero and Miranda made this disjuncture by showing him their language in any case. In this sense, they created Caliban's monster.