Mr. Weller, the elder, gave vent to an extraordinary sound, which being neither a groan, nor a grunt, nor a gasp, nor a growl, seemed to partake in some degree of the character of all four.

-- Charles Dickens, "Pickwick Papers"

To your spouse's breakfast-table query, you absent-mindedly answer: Mm-hmm.

Hearing a surprising tidbit of workplace gossip, you exclaim: Huh!

Reading the news of the latest political scandal, you click your tongue: Tsk, tsk, tsk.

Your child takes a tumble, and you offer a comforting syllable: Awww.

Panhandlers and presidents, preschoolers and Ph.D.s -- all conduct much of their conversation in meaningful grunts, hums and clicks. The almost-words that pepper informal speech are a critical but still mysterious element of human conversation. Some scholars believe they may offer a hint of how human ancestors communicated.

"These are the Cinderella elements of language," says Carl Mills, a sociolinguist at the University of Cincinnati. "They do a lot of work, but they're not fit to go to the ball."

Until a few decades ago, analysis of speech focused on semantics, the strict meaning of words and phrases. Beginning in the 1950s, linguists started to pay more attention to what came to be called "paralanguage" -- all the elements of speech that are not standard words: sounds of hesitation and exclamation such as "oh" and "um," "whew" and "ugh," as well as volume, accent and tone of voice.

Later, scholars broke off a subspecialty called "kinesics," the body language that can radically alter the meaning of a statement in context: an expressive raise of the eyebrows, a hostile crossing of the arms, a resigned shrug of the shoulders, a dismissive wave of the hand.

One of the few books devoted to paralanguage, a 1993 study by Fernando Poyatos, has chapters on "Shouting" and "Coughing and throat-clearing" and a whole section pondering "the morphology of the belch." And that's just the once-over-lightly version; Poyatos, now retired to his native Spain after a long teaching career in the United States and Canada, says he's at work on a three-volume work.

Poyatos' book particularly decries the "scholarly neglect" of "quasilexical segmental utterances," as he calls the meaningful grunts of paralanguage.

The uh-huhs and uh-ohs of American English, which have counterparts in most other languages, began to attract scholarly attention about the time tape recorders became widely available. Rarely appearing in print, they had been largely ignored. But recordings underscored their ubiquity in speech, including certain notorious conversations.

From a telephone call in March 1973: President Richard M. Nixon: ... the investigation has been conducted and we find this, that and the other thing and whack! Just like that. You see what I mean?

White House Counsel John Dean: Mm-hmm.

Or, from a body wire in January 1998:

Linda Tripp: Tell me the truth here, Monica.

Monica Lewinsky: Uh-huh.

Tripp: Do you believe that he would consider me better or a team player or a good political appointee --

Lewinsky: If you did that?

Tripp: Mm-hmm.

As transcripts and linguistics journals began to print these particles of conversation, dictionary writers created entries for them, classifying them with the grammatical label of interjection. "Sometimes these terms take longer to get in the dictionary because at first they're just in speech," says Karen Wilkinson, an editor at Merriam-Webster Inc.

But the dictionary entries have little to say about their origins or antiquity, which remain obscure. And definitions tend to illustrate the astonishing flexibility of the interjections. According to the Random House Unabridged, for instance, the tiny interjection "huh" is used to express "surprise, bewilderment, disbelief, contempt or interrogation."

Written language can't capture the nuances of intonation that produce all those variations. But any listener can easily distinguish a skeptical "Huh!" -- meaning "I'll believe that when I see it" -- from an impressed "Huh!" -- meaning "I didn't know that, that's interesting."

Some scholars consider such sounds the most primitive elements of language. "The word, 'Yes,' comes much, much later than the almost-word 'Uh-huh,' " says Alan S. Kaye, a professor of linguistics at California State University at Fullerton.

"These are learned by children before they learn words. They're the first thing children learn -- and the last thing adult foreigners learn," Kaye says.

That's because they don't necessarily cross cultures. To an English speaker, a sudden intake of breath implies a gasp of shock or fear. But in Scandinavian conversation, a sucking in of breath that sounds like "ya" is a way of assuring a conversation partner you are listening, as English speakers will mutter, "mm-hmm" from time to time, especially on the telephone. Linguists call it "back-channeling."

"It's like on CB radio, saying 'I'm reading you loud and clear, good buddy!' " says David Murray, a Washington anthropologist who has studied native American languages.

Another common use of interjections is as "place-holders," hesitation sounds that give the speaker a moment to think. English speakers use "uh" or "um," meaning: Don't give up, don't interrupt, I'm going to get to my point eventually. Russians similarly use the particle "vot"; Arabic speakers pause with the word "yahni."

Unlike ordinary words, such sounds are "semantically empty," Murray says. "It's hard to say what they mean outside the context of a conversation." But pronounced in mid-sentence, they can be rich with significance. "Uh I don't think so," can be much more emphatic than "I don't think so."

"We are all performance artists when we speak," he says.

One American interjection heard in every school cafeteria but still overlooked by dictionaries is "Duh!", which might be roughly translated as, "Everybody knows that, you moron." It sounds quite contemporary. But Kaye, at California State University, says it is at least several generations old, and probably derives from the same ancient root that links "dumb," "dull" and "dunce."

Historians of language have pet theories for the origins of various other interjections; one school says "uh-huh" and "uh-uh" were introduced to America by West African slaves. But whatever the variations, many linguists think the whole class of grunt-like interjections may be a vestige of ancient human language, perhaps resembling the cries and grunts of animals.

Bill Hopkins, a research scientist at the Yerkes Primate Center in Atlanta, says many animals have a repertoire of meaningful sounds. Vervet moneys, for instance, have three distinct alarm calls to warn, respectively, about eagles, tigers and snakes. "If you play a tape of the eagle alarm cry," he says, "the vervet monkeys look up at the sky."

Chimpanzees' vocalizations, still little understood, are probably much more complex, Hopkins says. But he is skeptical that contemporary human interjections, part of the extraordinarily rich flow of human conversation, have much to do with animal sounds -- or with early humans' speech.

Mills, at the University of Cincinnati, acknowledges that barring the unlikely discovery of tape recordings of cave men, there won't be proof. "I don't think it's a settleable argument," he says. But he says he nonetheless believes that the hard-working, emotive huhs of human talk "tap into an older system. It's more basic. It's probably where language came from."