Archived trivia from tv.com: Sheldon claims that the high-pitched noise he hears is an octave above middle-C, but the note that he hums is actually a C-sharp.

Archived trivia from tv.com: 

The correct spelling of "Qochbe'" (klingon for "To agree") is with a "Qo", not a "Ko".

When Howard chants "One of us, one of us" he is referencing Tod Browning's 1932 film, Freaks.

archived trivia from tv.com: 

Zsa Zsa Gabor was originally going to play Marsha but was replaced by Carolyn Jones. Gabor would go on to play the villainess Minerva in 1968 for the show.

Carolyn Jones previously appeared in the 1953 movie House of Wax with fellow Batman alumni Vincent Price who played Egghead.

She is best remembered as Morticia on The Addams Family which aired on ABC from 1964-66.

Another 2 castmembers of The Addams Family, John Astin who played Gomez, portrayed The Riddler in 2 episodes (Batman's Anniversary & A Riddling Controversy) and Ted Cassidy who played Lurch & Thing makes a window cameo in "The Penguin's Nest". 

Window cameo: Howard Duff makes a cameo as as Sam Stone, his character from the television series Felony Squad.