Cellophane over the toilet bowl. Decaf coffee in the "regular" carafe. Armed with these or myriad other schemes, an April Fools' Day prankster strikes. More than just a celebration of mischief—or a license for the boorish—the practical jokes and humor associated with this annual holiday actually play a role in the formation and maintenance of social bonds in small groups.

"Humor is a very strong way of sharing world views and expressing that you're on the same page," says Giselinde Kuipers, an anthropologist and sociologist at the University of Amsterdam in the Netherlands. Kuipers's research, described in Good Humor, Bad Taste: A Sociology of the Joke (de Gruyter Mouton, 2006) has revealed that one's sense of humor is not only subjective, but can vary widely based on gender, ethnicity, economic status and nationality.

For instance, cultural similarities among those in northern Europe and the U.S. may not extend into what tickles their funny bones, Kuipers wrote. In the Netherlands, U.K. and Germany a wide divide exists between what the highest and lowest socioeconomic groups find funny, although there is not much of a difference between the sexes. In the U.S. this trend is reversed: economic status has a minimal effect on what people find funny, but gender plays a significant role. Overall, European humor tends to be more ironic and brutal and generally not as playful as American humor, Kuipers says, which affects cultural views of April Fools' Day pranks.

"For most Dutch educated people, any April Fools' joke would be a little childish, distasteful and vulgar," Kuipers says. Northern Europeans are less likely to prank on the holiday than are Americans.

Regardless of one's cultural background, however, humor generally serves to bring groups together.

Laughter releases endorphins (the brain's "feel good" chemicals) as well as oxytocin, which seems to contribute to social bonding. Together, these neurochemicals are thought to promote positive relationships among people. But just as humor can bring people together, Kuipers says, it can also exclude individuals. April Fools' pranks automatically create an "in" group who are in on the joke and can thereby define itself, shutting out those who are not.

Pranks, however, are rarely billed as a group bonding experience, nor is that the perpetrator's motivation. Often, the main purpose is simply to poke fun at someone or something, Kuipers says. In this way pranks can be a relatively nonthreatening way to mock bosses, leaders and others in charge.

Jokes and pranks "are designed to show off the strength of the relationship by testing that relationship," says Moira Smith, an anthropologist at Indiana University Bloomington. "And you have to know a person pretty well to know their foibles and what is guaranteed to get their goat."

In addition, Larry Ventis, a psychologist at The College of William & Mary, says that many pranks have a mild undercurrent of aggression to them. Practical jokes are similar to the play-fighting seen in young animals. Neither party intends to inflict serious damage, and both partners typically seem to enjoy the symbolic exchange.

The joke's on two
Just as it takes two people to fight, it also takes at least two people to pull off a good practical joke. Smith's study on the role of the audience in humor, published in 2009 in the Journal of American Folklore (JAF), found that a prank's audience is an underappreciated aspect of humor. And there is a tremendous cultural pressure to pretend to understand or appreciate punch lines. "Humor is a positive moral trait," especially in the U.S., Kuipers says. "Americans even expect the president to have a sense of humor." This cultural encouragement to enjoy a good chuckle can make it all the more uncomfortable to endure the deafening hush when a joke falls flat.

Smith called this awkward silence "un-laughter" in the JAF study. "When laughter is expected and doesn't come, that's quite a moment," Smith says. The silence can be uncomfortable and even guilt-inducing. If the joke is aimed at you, however, you're expected to grin and bear it, no matter how offended you might be.

As for the victim of a practical joke, Kuipers says, recovering requires a shift in his or her mind-set, from taking the situation seriously to understanding that everything that happened was in good fun—and not everyone can manage that gracefully.

"In order to laugh along with a joke that's been played on you, you have to at least be able to temporarily put yourself in other people's shoes and look at yourself from their point of view," Smith says, which isn't always easy. "It's hard to get the distance to laugh at something when you're actually…[the brunt of the joke]," she says.

So how did April 1 become the day of pranksters and fools? Legend has it that the holiday originated with a switch in the calendar that moved the beginning of the year. Those people who incorrectly believed the year began in April were the first April Fools.

Smith disagrees. "I think it has more to do with the fact that it's spring," she says. Spring weather is notoriously unpredictable, and a day that calls for shorts and sandals can be followed by a blizzard. "Spring is a time of year that fools us anyway," Smith said, "You think that winter is gone and you pack your woolies away—and then surprise, you were wrong." Welcome to April.