During Saturday night’s “Rumble in the Air-Conditioned Auditorium” between Fox News host Bill O’Reilly and Comedy Central’s Jon Stewart, the two debaters addressed the notion of “media bias,” with Stewart pulling no punches while likening O’Reilly’s network to an autoimmune disease.

Responding to debate moderator E.D. Hill‘s question about whether there is a left-wing media bias, Stewart said: “I think that Fox News is an overreaction.”

“I don’t believe that ABC or NBC or CBS are activist organizations for liberal causes,” he explained. “I think Fox looks at those organizations and they are sort of an autoimmune disease against that.”