One of the things about Cousin Itt was that he couldn’t really be understood by anyone except his family. Other people who interacted with him or made their way into the house of the Addams family had no chance to work out what he was trying to say.
In order to create the unintelligible gibberish that comes out from under all that hair, one of the producers spoke random sayings and phrases, sometimes even random syllables, into a tape recorder, and then played it back at high speed. This lets most people realize that they weren’t supposed to be able to understand him.
Made for the TV Show
Most of the Addams family came to the “New Yorker” fully formed back in the thirties, but there's one exception. Cousin Itt – from Gomez's side of the family, was added to the television show in the sixties. It came at the suggestion of producer David Levy, though the reason for this is unknown.
Charles Addams eventually provided sketches of the character. Unlike the rest of the family, Cousin Itt doesn't live in the house, but he does frequently visit and has his own room when he wants to stay the night. Nobody knows what he looks like under all that hair, and we aren't likely to find out.
Left or Right?
During the television show, Thing was portrayed by actor Ted Cassidy, who also played Lurch. Seeing as how Thing was just a hand, you'd think that it would be nothing more than having your hand come out of a box to point at things for a joke.
And, well, that's more or less what the job was all about. Cassidy would sometimes get a bit bored doing it, so – without telling anyone – he would switch hands. We imagine it was caught during editing, but nobody really minded that much. You can also see Cassidy's arm during a few select shots when Thing reaches out of his box.
He Didn't Actually Speak French
Thanks to all the French sayings the character Gomez had, many people would walk up to John Astin and speak French to him, thinking that he could understand them. The problem was that he couldn't really understand French; he just knew those sayings or could recite the lines phonetically.
Maybe they thought he was actually his character, or maybe they thought Astin actually knew French. No such luck. In a related event, Ringo Starr of the Beatles once grabbed Astin's arm and started kissing his way up, similar to how Gomez would kiss Morticia. Astin stopped the Beatle halfway up the arm.
Inspiration for Their Characters
Some of the characters in this family aren't exactly your normal family members, and for the actors to be inspired, they had to take knowledge from a few strange places. In order to play Morticia in the first two movies, Anjelica Huston watched “Grey Gardens,” a 1975 documentary about a pair of strange women, mother and daughter, who had lived in a big mansion by themselves.
It's considered a masterful documentary. In addition, Christina Ricci based her performance of Wednesday from the same movie off Winona Ryder's performance from “Beetlejuice,” which had come out a few years earlier. Being a dark, spooky girl when you're actually a charismatic actress isn't the easiest thing.