Leonard recounts his early Christmas experiences where he had to leave Santa Claus a research paper, which would then be graded. This is consistent with his account in The Maternal Congruence (2009), where during Christmas, everybody had to write research papers on the anthropological and psychological implications on human society, after which they broke off into focus groups and critiqued each other.
Bernadette's working uniform is shown again. On the left chest there is a blue "ZANGEN" sign in an ellipse.
Sheldon says he kicks Santa in his "Bowl full of jelly." Chandler says this on an episode of Friends (1994). Kaley Cuoco is a huge Friends (1994) fan.
The Jingle Bells bells are in no noticeable order among the participants. Left to right: Howard plays 2 & 1; Stuart plays 3 & 6; and Sheldon plays 5 & 4 (i.e. stage right to stage left).