Everyone enjoys the occasional practical joke – assuming the gag isn't mean-spirited or overly perilous, even the prank's poor victim can appreciate the punch line!

I'm sure you have your favorites: gluing dollars to sidewalks, filling your co-worker's office with balloons, moving your roommate's bed to the basement… while he’s sleeping in it.

More typical stunts may employ whoopee cushions, fake vomit, and hand buzzers, but honestly, those are a tad sophomoric and overdone. Thus, in an effort to elevate the standard of stunts, I'd like to present a gag that makes use not of stink bombs, but of science.

How to implant false memories in your friends, in four steps:

In The Demon-Haunted World, Carl Sagan argued that implanting false memories in people is not only possible, but is actually pretty easy when attempted in the proper settings with a gullible subject, He cited as examples people who, at the urging of therapists or hypnotists, genuinely start to believe that they'd been abducted by UFOs or falsely remember being abused as a child. For these people, the distinction between memory and imagination becomes blurred, and events that never actually took place become sewn into their memories as real events. They can even describe these false remembrances incredibly vividly – as if they actually happened!

"Memory can be contaminated," Sagan wrote. "False memories can be implanted even in minds that do not consider themselves vulnerable and uncritical."

Sagan's insight provides a segue into step one of our plot to implant a memory, which is made possible by a frank fact: your friends -- while undoubtedly honest, funny, supportive, and intelligent -- probably don't all possess invulnerable and critical minds. Thus, the first step is to select one of your mates who, in your estimation, is "prone to suggestion." Please note that you should be acquainted with this friend for at least five years, and have shared experiences with him or her. This will enhance your believability, and thus your odds of success.

Once you've got your target singled out, the next, and possibly the most critical step, is to fabricate a memory. The false memory should have "taken place" at least a year in the past, not be unduly intricate, and not be something that might engender strong feelings of emotion.

Studies have shown that it's easy to make people falsely recall small details about events, but as the fake memories grow in complexity and specificity, implantation grows progressively harder, though not impossible. After three interviews, researchers at Western Washington University succeeded in getting subjects to recall details about accidentally spilling a bowl of punch on the parents of the bride at a wedding reception. As described by University of Washington psychologist Elizabeth Loftus in a 1997 article for Scientific American:

During the first interview one participant, when asked about the fictitious wedding event, stated, "I have no clue. I have never heard that one before." In the second interview the participant said: "It was an outdoor wedding and I think we were running around and knocked something over like the punch bowl or something and um made a big mess and of course got yelled at for it."

Emotions tend to make people remember associated events more vividly. (You probably can recall where you were and what you were doing around the time of traumatic events, for example.) Thus, your target might not be as apt to accept a false memory if you told him or her that they experienced something highly emotional. In 1999, researchers at the University of British Columbia did succeed in convincing 26% of their subjects that they had been victims of a vicious animal attack in their childhood, but the research team's sophisticated methods probably won’t apply in a practical joke setting.

Choosing a childhood memory will give you the best odds of success. You'll have an easier time implanting something that supposedly occurred far in the past. Since this is meant to be a practical joke, I recommend creating a false memory that's comical and not potentially life-scarring.

If you want more of a challenge, try to implant a memory that supposedly occurred more recently. For example, you could concoct a scene at a bar in which you purchased your friend a plethora of drinks and he or she never paid you back. That way, should you succeed, you'll get some money out of the deal (…which you will, of course, give back once you reveal your playful deception).

With the memory and target selected, your third task is to prepare. You're going to need a couple things if the prank will have any chance of success. First off, you'll need to formulate some narrative details surrounding the false memory. Be as specific as possible. What outfit was your friend wearing? What were the circumstances that led to the event? What was the setting like? Who was there?

If you're skilled at editing images, you could also try doctoring a photo. In 2002, psychologists exposed twenty subjects to a false childhood event using a fake photograph. Over three interviews, subjects were instructed to think about the photo, which showed them on a hot air balloon, and were made to recall the event with guided-imagery exercises. At the study's conclusion, fifty percent of subjects ended up concocting complete or partial false memories!

You'll also need corroborators; the more the better. The power of corroboration in instilling false memories was demonstrated in the 1990s by researchers at Williams College. In their study, participants were falsely accused of causing a computer to crash by pressing a wrong key. According to Loftus:

"The innocent participants initially denied the charge, but when a confederate said that she had seen them perform the action, many participants signed a confession, internalized guilt for the act and went on to confabulate details that were consistent with that belief."

Now you're ready to set your plan in motion. When you commence, be persistent. The memory may not stick right away; you'll probably have to bring it up multiple times over a span of days or even weeks. Additionally, don't be afraid to use peer pressure. You and your compatriots should utilize phrases like the following:

"Really? You don't remember that?"

"Seriously? You were there!"

"Your memory is awful!"

Memory isn't static. It's fickle, ever changing, and easily tampered with; a patchwork quilt that can be ripped, torn, and remade.

"Perhaps what we actually remember," says Carl Sagan, "is a set of memory fragments stitched onto a fabric of our own devising. If we sew cleverly enough, we have made ourselves a memorable story easy to recall."

Still, implanting a false memory in a person, and having them fully believe it, takes some doing. Even in the lab, researchers succeed less than half of the time…

…but it can be done. So sew away, my friends. Sew away.

Images: Balloons by Tomascastelazo / Wikimedia Commons, Imagination by Mehdinom / Wikimedia Commons.