Ralph

“[On the subject of Heath Ledger's Joker] This character who attracts psychotic henchmen may have lingering symptoms from his own past psychosis. He keeps making involuntary, repetitive movements—flicking his tongue, smacking his mouth—which suggest tardive dyskinesia, a condition that arises as a consequence of long-term or high-dosage use of antipsychotic (neuroleptic) medication.”
― Travis Langley, Batman and Psychology: A Dark and Stormy Knight