Courage the Cowardly Dog - Season 3 Episode 15
So In Louvre Are We Two

Courage, Muriel, and Eustace win a trip to an art museum in Europe. Muriel talks about how her mother aways said that Muriel aways looked liked the Mona Lisa. They go into the museum right before closing time and then get locked in. They fall asleep in their and when they wake up Muriel walks up to the painting of the Mona Lisa and gets pulled in. Then the Mona Lisa steps out of the painting (the plantets align and the portrait people switch places with real people) Eustace switches places with the thinker and Courage has to chase down the Mona Lisa so he can get Muriel back. The Thinker and the Mona Lisa go on a date into some portraits. Courage and Muriel enter a painting of what they say looks like there house (and it is) and they sit there at home wondering where Eustace is?