because the music / is boring me to death: Tethys and Titan, photographed by Cassini, 11th December 2011.
Cassini takes photographs through red, green, and blue filters, which can be combined to create colour images. Part of the process is aligning the colour layers where the target has moved between photographs. And when the images contain two moving targets, then you need to get fancy.
Lower left gif shows composite aligned to Titan. Lower right gif shows composite aligned to Tethys. Main gif combines the colour image of each moon from its composite, using the positions in the red images.