Jerry Seinfeld will do a "pop-in" on his old friend, Larry David, this season on Curb Your Enthusiasm.

"But don't blink," David told Newsweek for next week's issue.

David said the comedian, with whom he created Seinfeld, showed up during an episode set in Manhattan and makes a brief cameo, but wouldn't elaborate.

The fourth season of the HBO comedy, which began Sunday night, stars David as himself: a cranky comedy writer. He figured he'd do 10 episodes a year, compared to the 23 required for a network series, and that production would take eight months at the most.

But even though the shows are mostly improvised, he found that writing 10 episode outlines takes so long, he has to start on a new season as soon as he finishes the last one.

"I'm working all the time," the 56-year-old said. "It's 51 weeks a year. I'm working more days on this show than I did on Seinfeld. It's not OK at all! It's the opposite of OK!"