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This might be the perfect retort to ‘Crooked Hillary’ or ‘Sleepy Joe’

Co-opting your opponent’s line rather than ignoring it could neutralize its power.

A fictional ad used in an experiment that measured the poison parasite effect. Here an ad for a made-up candidate, Walter McKinley, is reused by his opponent, who has added rebuttals in red to McKinley's original black text.
A fictional ad used in an experiment that measured the poison parasite effect. Here an ad for a made-up candidate, Walter McKinley, is reused by his opponent, who has added rebuttals in red to McKinley's original black text.Courtesy of Jessica Lasky-Fink et al.

What can you do if a deep-pocketed political opponent is lying in their ads? You might think the best response is to ignore the lies. But some social psychologists say you should embrace them. In fact, grab onto your opponent’s message and hitch a ride, like a hungry tick on a passing ankle.

Researchers call this the poison parasite defense, and it harnesses the power of associative memory.

Harvard Kennedy School behavioral scientist Todd Rogers and coauthors demonstrated how this might work in a new study that hasn’t yet been through peer review. The key is to tie your own message to some element of your opponent’s campaign. It should be something they repeat often — maybe an image or a phrase. If you use that image or phrase in your own counter-message, they’ll be linked in a viewer’s memory. Every time afterward that viewers see your opponent’s ad, it will remind them of you.

“You start free-riding on your opponent’s attacks,” Rogers says. “When they attack you, they then also bring to mind everything you’ve tied to their attack.”


Rogers learned about the idea of the poison parasite more than a decade ago from Robert Cialdini, now an emeritus professor of psychology and marketing at Arizona State University. Rogers says he loved the idea and often asked Cialdini for updates on the research. Finally they decided to collaborate on a study.

The team demonstrated the power of the poison parasite in a series of experiments. In one, they showed subjects a print-style ad for a fictional political candidate named Walter McKinley. The ad displayed claims about McKinley’s achievements (such as “helped create more than 5,000 jobs”) over a circular American flag background. Then some subjects saw a response ad with counterarguments to McKinley’s claims (like “All of the jobs McKinley created were TEMPORARY and OUT OF STATE”) against an image of a crowd of people. Other subjects saw a poison parasite ad. It was McKinley’s original American flag ad, with the counterarguments overlaid in red text, as if a teacher had marked up a bad essay.


The poison parasite ads were much more effective at countering the opponents’ claims. Subjects who saw the poison parasite ad against McKinley, for example, afterward considered him less honest and said they were less likely to vote for him.

And the effect was surprisingly long-lasting, Rogers says. Even two weeks after subjects saw the poison parasite ad, seeing McKinley’s own ad seemed to remind them why they didn’t like him.

A poison parasite defense may work best “when one side is louder than the other,” Rogers speculates. Rather than being drowned out, “the weaker side can parasitically attach to the stronger side’s messages, and in the process have their opponent carry their message along for them.”

Although the experiments in this study all used visual memory cues, you could in theory also tie a poison parasite to a verbal cue. For example, maybe you have a political opponent who really likes giving people nicknames.

“Trump has not been as disciplined this election cycle as he was in the last one in terms of phraseology,” Rogers says. “But in 2016 it was always ‘Crooked Hillary.’” Clinton ignored the nickname, but she might have had success attaching a poison parasite to it instead. For example, Rogers suggests, Clinton could have said, “When he says ‘Crooked Hillary,’ remember that he has actually defrauded nearly everyone he has associated with.”


Still, Rogers doesn’t think presidential campaigns are the most promising venue for a poison parasite defense. Voters have already been saturated with information from both sides. He thinks the strategy might be more powerful with ballot initiatives, like the two that Massachusetts voters are considering this fall. Voters are usually not as well informed about these initiatives, and there’s often a lot of funding behind one side, Rogers says.

The researchers have made a convincing case for the poison parasite defense in their experiments, says Joshua Compton, who studies the science of communication at Dartmouth College and wasn’t involved in the study. “It seemed to work really well.”

Compton says the idea is similar to one called inoculation theory. In that strategy, preemptively exposing people to a weaker version of an argument helps them resist it later on, much the way a vaccine uses a weakened virus to help you fight future infections. It’s commonly used in politics, marketing, and health communication, Compton says — any time the message is, “The other side will tell you this, but here’s the truth.”

He’s eager to know how the poison parasite defense might work in other realms. There’s no reason its success should be unique to politics and advertising, Compton says. Could it also help fight against scientific misinformation, such as about climate change or vaccines?

“We have tons of research looking at what can make us more persuasive,” Compton says, “but comparatively little about what can make us less persuadable.”


Elizabeth Preston is a science journalist in the Boston area.