"Saint Vitus' dance" is a kind of chorea,
the medical term for a neurological disorder causing
involuntary, quick, spasmodic movements of the body's muscles.
(Chorea comes from the ancient Greek choreia =
dance.) In recent medical practice Saint Vitus' Dance, which
affects the feet, hands, and face, has come to be known as
Sydenham's chorea. It often afflicts children who have had
rheumatic fever or other streptococcal infections.
Saint Vitus was an early Christian martyr whose feast day was
celebrated, in some parts of Europe during the later Middle
Ages, by dancing before the saint's statue. (Perhaps
coincidentally, his feast day is June 15.) Vitus became the
patron saint of dancers and epilectics.
The grotesque pseudo-dancing of "A deafmute idiot
with goggle eyes" helps set the scene of this
chapter's Walpurgisnacht,
in which half-crazed people stumble through a hallucinatory
cityscape, surrendering to mad random jerks of thought and
imagination. Trapped within a dysfunctional body, the boy also
introduces the reader to the Homeric condition of Circean
enchantment, in which rational individuals are plunged into
groteque animal corporeality.