It probably won't shock you that the most popular YouTube video in the past month was "Gentleman," the latest hit from South Korean rapper PSY, whose "Gangnam Style" is the most-watched video of all time. More surprising: among the other most-watched videos was an advertisement for bottled water.

Evian's baby&me features several adults dancing with toddler versions of themselves in the reflection of a store window. Only at the end of the 77-second video do we see a bottle of Evian, along with the slogan "Live young." Since its release in April, the video has garnered more than 53 million YouTube views. By contrast, Nestlé's self-explanatory "From Maine Water Springs to You: The Journey of Poland Springs Water" has barely cracked 500 views. So why did one water commercial sparkle on YouTube, while the other fizzled?

The answer may lie at the heart of new research by Thales S. Teixeira, which identifies the ingredients necessary to create online videos so compelling that viewers will not only want to watch them but also actively seek them out and share them with friends, family, and coworkers. The research shows that if sharing an ad will somehow benefit the sender as much as it helps the advertiser, then the ad might go viral.

The stakes are high for advertisers. eMarketer estimates that online video advertising in the United States will increase from $1.1 billion in 2009 to $4.1 billion in 2013—an overall spending rise from 4.3 percent to 11.0 percent of all advertising expenditures. Advertisers can get the most bang for the buck if they post their videos on YouTube and then motivate consumers to disseminate the ads for them, via email or social media. Getting an ad to go viral is among the cost-saving techniques that fall under the umbrella of what Teixeira terms lean advertising. (Other lean advertising techniques include do-it-yourself content, crowd-sourced talent, and do-it-yourself distribution—also known as inbound marketing.)

"It turns out that while getting people to watch an ad is all about emotion, getting them to share it is about the sender's personality.”

So how do firms increase the likelihood that their ads will go viral? For starters, they need to prioritize entertainment over facts and figures. To paraphrase an old campaign, these are not your father's Oldsmobile ads.

"People no longer want a lot of information about the products or brands in the advertisements they watch," says Teixeira, an assistant professor at Harvard Business School who has spent the last four years figuring out the factors that make or break online ads. "In the past, when a company launched a new product, the advertisement would include all the information about the product so you could discover whether you wanted to buy it. But now we have all the information about all the new products available to us online. Now, we want ads to entertain us."

But making an ad go viral requires more than mere entertainment. According to Teixeira's research, successful viral advertising requires four key steps: attracting viewers' attention, retaining that attention, getting viewers to share the ad with others, and persuading viewers. "The issue is that some content is better at the first stage, some is better at the second stage, some is better at the third, and some is better at the fourth," says Teixeira, who will deliver a lecture explaining how to foster each step at the Cannes Lions International Advertising Festival on June 20. "The challenge lies in getting the best mix of all four ingredients and baking them into your ad."

Tapping Into Consumers' Personalities

Teixeira discovered the keys to attraction and retention through a series of lab experiments where participants viewed real ads that Teixeira selected from YouTube, while a camera recorded their facial reactions. They had the choice of watching an entire ad or skipping to the next one at any time. Researchers collaborating with Teixeira then measured the participants' emotional responses with a combination of eye-tracking technology and facial expression analysis software.

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The data showed that evoking surprise was the best way to attract attention, while evoking continuous moments of joy was the best way of retaining it. Thus, the most captivating ads in the experiment were those that began by surprising the viewer and then went on to make the viewer smile.

But successfully capturing and keeping viewers' attention during a YouTube video does not guarantee that they will share it. "People watch a lot of things online that they would never share with anyone," Teixeira notes.

To figure out what prompts viewers to share ads, Teixeira's team conducted an additional experiment where participants could forward ads to their friends outside the lab. The researchers tagged the videos in order to keep track of which ones were shared. Participants also completed written personality tests to gauge whether they were introverts or extroverts, self-directed or other-directed.

"It turns out that while getting people to watch an ad is all about emotion, getting them to share it is about the sender's personality," Teixeira says.

After comparing the sharing behavior with the emotional responses and personality tests, Teixeira found that the main motivation for viral sharing was egocentricity—the viewer's desire to derive personal gain from sharing the video. In this case, the potential gain comes in the form of improving the viewer's reputation among friends and family, for example. Thus, it behooves advertisers to create videos that not only will make the product look good but, if shared, will make the viewer look good, too. Teixeira refers to this idea as "advertising symbiosis" because the advertiser and the viewer mutually benefit from the act of sharing.

Five Examples Of Advertising Symbiosis

Teixeira offers five approaches as examples to achieve virality through advertising symbiosis:

CONCEPT: Make the viewer the center of attention.

EXAMPLE: Old Spice's Twitter campaign. In 2010, Procter & Gamble launched a campaign where Facebook and Twitter users were encouraged to send messages to Isaiah Mustafa, the strapping spokesman for Old Spice who markets the idea that if men can't look like him, they at least can smell like him. The advertising agency Wieden+Kennedy then created and uploaded 185 short videos where Mustafa responded personally to individual Twitter users, a mix of celebrities, politicians, and average fans. Inevitably, they supposedly shared the personalized responses with their social networks, and many of the videos received upwards of a million views each.

In 2010, Procter & Gamble launched a campaign where Facebook and Twitter users were encouraged to send messages to Isaiah Mustafa, the strapping spokesman for Old Spice who markets the idea that if men can't look like him, they at least can smell like him. The advertising agency Wieden+Kennedy then created and uploaded 185 short videos where Mustafa responded personally to individual Twitter users, a mix of celebrities, politicians, and average fans. Inevitably, they supposedly shared the personalized responses with their social networks, and many of the videos received upwards of a million views each.

CONCEPT: Offer the viewer privileged access to valuable content.

EXAMPLE: Virgin Atlantic's sneak peek. Also in 2010, members of Virgin Atlantic's frequent-flyer program received an email message with a link to the airline's new commercial on the web. The ad wouldn't air on TV for another week, the customers learned. The airline was giving them the privilege of a sneak peek at the ad—and the privilege of being among the first to share it.

Also in 2010, members of Virgin Atlantic's frequent-flyer program received an email message with a link to the airline's new commercial on the web. The ad wouldn't air on TV for another week, the customers learned. The airline was giving them the privilege of a sneak peek at the ad—and the privilege of being among the first to share it.

CONCEPT: Give the viewer the opportunity to communicate his or her values to others.

EXAMPLE: Dove's message about self-image. Two months ago, Unilever's Dove brand uploaded "Dove Real Beauty Sketches," a web-exclusive mini-documentary in which a forensic artist sketches each of several women twice, first based solely on their descriptions of themselves and then based on descriptions from strangers. The women are seated behind a curtain, hidden from the artist's view. Side-by-side comparisons of the sketches inevitably reveal that the sketches based on the strangers' descriptions are more stereotypically attractive than the sketches based on the women's descriptions of themselves. The powerful tagline, accompanying a Dove logo: You are more beautiful than you think. (Evian's "live young" campaign delivers a similarly positive message—not to mention the fact that dancing babies garner the magic mix of surprise and joy.) "I think of these types of ads as video bumper stickers," Teixeira says. "They let people broadcast their personal values the way a bumper sticker on the back of a car does."

Two months ago, Unilever's Dove brand uploaded "Dove Real Beauty Sketches," a web-exclusive mini-documentary in which a forensic artist sketches each of several women twice, first based solely on their descriptions of themselves and then based on descriptions from strangers. The women are seated behind a curtain, hidden from the artist's view. Side-by-side comparisons of the sketches inevitably reveal that the sketches based on the strangers' descriptions are more stereotypically attractive than the sketches based on the women's descriptions of themselves. The powerful tagline, accompanying a Dove logo: You are more beautiful than you think. (Evian's "live young" campaign delivers a similarly positive message—not to mention the fact that dancing babies garner the magic mix of surprise and joy.) "I think of these types of ads as video bumper stickers," Teixeira says. "They let people broadcast their personal values the way a bumper sticker on the back of a car does."

CONCEPT: Enable the viewer to showcase a badge of honor and relate to tribes.

EXAMPLE: Fiat's rapping mommy. Last December, Fiat UK released "The Motherhood," a hip-hop video in which a British mother raps about the joys and indignities of being a mom. ("I swapped my sexy handbag for a snot-stained sack…") The Fiat 500L makes a cameo appearance, but her life is the focal point. The idea is that moms will share the ad with other moms. "Fiat is not really about mothers, but the company is providing the connection among them," Teixeira explains.

Last December, Fiat UK released "The Motherhood," a hip-hop video in which a British mother raps about the joys and indignities of being a mom. ("I swapped my sexy handbag for a snot-stained sack…") The Fiat 500L makes a cameo appearance, but her life is the focal point. The idea is that moms will share the ad with other moms. "Fiat is not really about mothers, but the company is providing the connection among them," Teixeira explains.

CONCEPT: Let viewers show off their ability to find strange hidden gems.

EXAMPLE: Blendtec's wacky blender videos. In 2006, Blendtec founder and CEO Tom Dickson launched a series of infomercials where he sticks an object in the company's flagship Total Blender and answers the question, "Will it blend?" Items he has blended in the series include an iPhone, an iPad, a can of Easy Cheese, and a vuvuzela. Unlike many viral ads, this one features the product front and center. Usually that's a turnoff, Teixeira says, but these videos are too fun and unconventional not to share.

As for persuasion, the final step of successful virality, marketers (with the notable exception of Blendtec) face the tough challenge of entertaining viewers without losing a connection to the brand. Showcase the brand too much and viewers will stop watching, not enough and they won't know what the video is advertising. The solution, based on Teixeira's research, is a technique called "brand pulsing," wherein the brand or product is shown repeatedly but not too intrusively throughout the course of the video.

And if it produces a strong emotional response, the video—and the brand—might stick with the viewer for a long time.

"When entertainment creates an emotional connection, it leaves a lasting effect on our minds," Teixeira says. "Psychologists have shown that emotions are memory markers, and if you feel very strongly about something during the day, your brain will more likely retain the information related to that emotion longer."