The Slovenian philosopher Slavoj Žižek turned up at Zuccotti Park to address the Occupy Wall Street demonstration on Sunday, offering up a seminar on Radicalism 101 for an appreciative crowd.

Despite some difficulty with the Human Microphone—the sometimes unwieldy but strangely appealing system the protesters have adopted of repeating a speaker’s words, phrase by phrase, for the benefit of the crowd—he held the floor for the better part of an hour.

Standing above the assembly in a red T-shirt, the heavily bearded dissident–turned–academic superstar at first spoke from prepared notes, hitting on many themes that will be familiar to fans. Several riffs were recycled almost word-for-word from earlier talks included in the 2005 documentary Žižek!, but to be fair, they killed at the time and are perhaps even more relevant today.

He told, for instance, an old Eastern Bloc joke (borrowed from the introduction to 2002’s Welcome to the Desert of the Real) about a dissident who’s about to be sent to a work camp in Siberia. Since he knows his letters will be censored, he tells his friends he’ll write to them using a simple code: Blue ink for the truth, red ink for lies. His first letter arrives, and it’s a glowing report of life in the camp—a lovely apartment, great food, beautiful women. Then he concludes, “The only thing we can’t get is red ink.”

Occupy Wall Street, he explained told the crowd, is pointing out the lies that underlie American capitalist society. “You’re the red ink,” he said.

Mr. Žižek also offered some practical advice. Noting the festive atmosphere in the park, he warned, “Don’t fall in love with yourselves. Carnivals come cheap.” The meaningful work will be what comes afterwards.

He steered the discussion away from the Cold War debate between communism and capitalism, noting that former communists, particularly in China, “are today the most efficient, brutal capitalists.”

The communist revolution “failed absolutely,” he said, suggesting that “the only way we are communist is that we care about the commons,” citing the environment as an example.

Mr. Žižek suggested that the left “abandon certain taboos,” including hard work, discipline and following orders, if they support the agreed-upon goals. And he advocated reclaiming certain notions that had been adopted by the right wing, including family values.

Somewhat controversially, he described organic food as a “pseudo-activity,” designed to make consumers feel they are having a positive impact on the world and thereby absolving them from looking at the more destructive systemic issues.

Noting that he supports George Soros, he compared the lefty billionaire financier to a chocolate laxative. Since chocolate is said to be constipating, he explained—a controversial point—Mr. Soros is similarly exhibiting an internal contradiction. “First they take billions from you, then they give back half,” he said. “And that makes them the world’s greatest humanitarians.” Take the money, sure, he advised, but don’t stop fighting to overturn a system that makes it necessary.

In answer to one question, he suggested that Organize Wall Street embrace the Tea Party rather than be seen as its opposite. “The tragedy is that many of the Tea Party people should be on our side,” he said. “That’s where we should work. They may be stupid, but don’t look at them as the enemy.”

The most interesting bit of advice may have been a little hard to parse for some, but given that this quickly spreading movement seems still to be in its infancy and unsure about how to proceed, it seemed especially worth pondering: “People often desire something but don’t really want it,” Mr. Žižek told the crowd. “Don’t be afraid to want what you desire.”