Sheldon (Jim Parsons)'s Van Dyke is identical to that worn by a parallel-universe Mr. Spock from the 1960s, and contrasts starkly with the barbarian-like - or Klingon-like? - beards and hair on Howard (Simon Helberg), Leonard (Johnny Galecki) and Raj (Kunal Nayyar). Also, Howard and Leonard are compelled to curse Sheldon's "Vulcan hearing".
Leonard preserves a snowflake in a solution of polyvinyl acetal resin (also known as Formvar or Vinylec). This is a real thing. The trick was invented in 1940 by a General Electric researcher in Schenectady, NY, who adapted a technique used to cast copies of aluminum crystallization patterns. Before then, snowflake patterns could only be captured with microphotography.
Just before the first shot of Sheldon with his mother in Texas, there is one of the shots of atoms used to separate scenes. One of the electrons orbiting the nucleus is decorated with the Texan flag.
In the commentary for this episode on the DVD release, the actors actually grew real beards for filming, but they were told to shave them so that the make-up department could put fake ones on. It is never stated why this decision was made.
The movie Toy Story (1995) is mentioned by Raj just before he, Leonard, and Howard approach Mary Cooper's house. This refers to Howard's outfit resembling Woody's outfit from Toy Story. Mary Cooper is played by Laurie Metcalf, who did the voice of Andy's mother in Toy Story and its sequels.