"Mona ___," painting with an enigmatic smile
I believe the answer is:
lisa
(Other definitions for lisa that I've seen before include "Mona ..., also called La Gioconda" , "Mona . . . ., famous painting by Leonardo da Vinci" , "Leonardo da Vinci painted the 'Mona ....'" , "Most intelligent of Marge Simpson's children" , "Girl" .)