Penny: Hey, Sheldon, are you and Leonard putting up a Christmas tree?
Sheldon: No, because we don't celebrate the ancient pagan festival of Saturnalia.
Howard: Gather round, kids, it's time for Sheldon's beloved Christmas special.
Sheldon: In the pre-Christian era, as the winter solstice approached and the plants died, pagans brought evergreen boughs into their homes in an act of sympathetic magic intended to guard the life essence of the plant until spring. This custom was later appropriated by northern Europeans and eventually becomes the so-called Christmas tree.
Howard: And that, Charlie Brown, is what boredom is all about.