When Raphael leaves a manhole to go to a party, a second image of him is left in the manhole.
The Ninja Turtles are each named after the four artists from the Renaissance period (Leonardo is named after Leonardo da Vinci, Raphael is named after a famous painter of the same name, etc.) and Mona Lisa is named after the woman of the same name of what would become the world's most famous painting over time done by the late Leonardo da Vinci. It hardly makes that any turtle other than the one named after the painter behind such painting to be in a relationship with the individual named after said painting.