Silmarillion

When the Eleventh Doctor was on the verge of drowning, he wondered if he could regenerate into something with gills like silmarillions. (PROSE: Dark Horizons)

Behind the scenes

 * is a collection of stories by J. R. R. Tolkien about three jewels known as the Silmarils.
 * "Silmarillions" is uncapitalised in the text of Dark Horizons.