From my rematch - a Christmas postcard! There's a Christmas-y graph on the front, and a note from the sender saying that they are a 5th year astrophysics student in Holland. I LOVE puns, so I think this card is relatively perfect!

Small print on postcard: "This postcard shows the Schwarzschild metric from the theory of general relativity, which describes the gravitational field outside of a spherical mass. (Like a planet or star, or in this case a not so spherical Christmas gift!) The green lines represent spacetime, which curved under the gravity of the gift."