Sean Penn was among the many A-list guest stars who appeared on Friends during its iconic run. According to Lisa Kudrow, his presence on set unexpectedly triggered a peculiar reaction from co-star Matthew Perry.

Perry, Kudrow, and Matt LeBlanc had an ongoing joke involving sneaking up on each other to "ambush tickle" one another. Kudrow explained the dynamic during an appearance on The View on Thursday, promoting season 3 of The Comeback.

"It’s terrifying. And someone would be lurking, you know, they walk by and (flinches) you just went like that," Kudrow recounted.

The actress recalled a specific episode where Perry’s anxiety peaked: The One With the Halloween Party. Penn guest-starred as Eric, Phoebe’s (Kudrow) twin sister Ursula’s boyfriend. The episode remains a fan favorite, particularly for Perry’s Chandler, who was dressed in an oversized pink bunny costume when he suspected Penn was joining in on the tickle ambush.

"He walked by Matthew and Matthew went ‘WOAH!’ And then came over and said ‘Just thought Sean Penn was gonna try to tickle me,’" Kudrow shared. "We laughed so hard, of course Sean Penn wasn’t gonna tickle him!"

She added, jokingly mimicking Penn’s reaction: "It was just a funny, at the time. Sean Penn would go ‘Woo!’" The absurdity of the situation left Kudrow and the cast in stitches. "It didn’t make sense," she concluded.

Source: The Wrap