Don't laugh, but professor Chris Westbury's newest psychology study is about farts.

It's also about snots, chortles, wienies, heinies and bozos; things that are wriggly, jiggly, flappy and slaphappy; things that waddle, things that slobber; things that puke, cluck, squawk and dingle.

That's because Westbury studies funny words — and, more specifically, what makes some words funny and others not.

"As schoolboys of a certain age rediscover repeatedly, there is a sense in which simply uttering the word fart is a one-word joke," Westbury and Geoff Hollis, both professors at the University of Alberta in Canada, wrote in a new study published Oct. 18 in the Journal of Experimental Psychology: General. [Does It Fart? 10 Fascinating Facts About Animal Toots]

But what, Westbury wondered, makes the word "fart" so funny? He already knew from a 2016 study he co-authored that part of a word's funniness could be explained by the popular theory of humor known as incongruity theory — the idea that something becomes funnier the more it subverts your expectations. In that study, students rated the funniness of several thousand meaningless, computer-generated words, or "nonwords." The nonwords with surprising letter combinations that looked least like known English words — such as "snunkoople," "hablump" and "jumemo" — were consistently rated funniest.

Dirty-sounding nonwords like "whong," "dongl" and "focky" also performed very well, suggesting that a word's perceived connotation played a role in humor, even for words that had no real meaning. In their new study, Westbury and Hollis delved further into the relationship between word sounds, meanings and humor — this time, working with tens of thousands of real English words.

The science of booty tinkles

They started with a list of 4,997 common words previously compiled by a team of psychologists at the University of Warwick in the U.K. and scored with funniness ratings by a panel of 800 online participants. The Warwick psychologists found that words like "booty," "tinkle" and "nitwit" were consistently ranked as being very funny, while words like "pain," "torture" and "deathbed" were ranked as being decidedly humorless.

Westbury and Hollis looked at each one of the nearly 5,000 words under a humorist microscope, categorizing them based on 20 different factors, including how long the word itself was, how positive or negative the word's meaning was, how common each letter or combination of letters was in English, and whether the word contained a crude or profane-sounding string of characters within it (like "pike" and "bunghole," for example).

With these factors and the pre-existing humor scores for the words in the entire list, the researchers devised several different equations that could, theoretically, predict the humorousness of any given word. They tested two of their humor equations on a list of more than 45,000 words, then ranked the results in their new paper. One algorithm decided the top five funniest words on the list were:

1. Upchuck

2. Bubby

3. Boff

4. Wriggly

5. Yaps

The second equation, which was written with the help of a special data-modeling program Hollis and Westbury co-created in 2006, predicted the funniest words were:

1. Slobbering

2. Puking

3. Fuzz

4. Floozy

5. Cackling

Among the highest- and lowest-rated words, several clear patterns emerged. Both equations agreed that the least-funny words were those with highly negative meanings — such as "violence," "attacks," "rape," "murder" and "harassment." Meanwhile, words with meanings related to sex, bodily functions, insults, animals and partying were consistently predicted to induce giggles (actually, "giggle" was the seventh-funniest word in English, according to the first data model). [Why We Laugh at Disgusting Jokes]

Word sounds (or "phonemes") played a huge role, too. Echoing Westbury's 2016 nonword study, words with an emphasis on relatively uncommon letters — like k, j and y — consistently appeared funny. The single funniest phoneme in English turned out to be the vowel sound /u/, as in "guffaw," "humph" and "lummox." This vowel sound appeared in nearly 20 percent of the words judged most funny, the authors wrote.

The perfect funny word, the authors concluded, is "a short, infrequent word composed of uncommon letters," and has a meaning that is "human and insulting, profane, diminutive and/or related to good times."

With that much settled, Westbury and Hollis hope to extend their research into quantifying the humor values of word pairs — "such as toothy weasel, muzzy muffin and fizzy turd," they wrote — and eventually entire jokes. How funny is a chicken crossing a road, anyway? Evidently, that depends on whether it farts on the other side.

Originally published on Live Science.