TV Article 'Grey's Anatomy' actor Jesse Williams guest stars on 'Sesame Street' By Emily Rome Published on October 16, 2013 08:13PM EDT Photo: Jesse Grant/PBS For Sesame Street visitors of all ages, characters like Elmo, Grover, and Cookie Monster aren’t just pieces of felt and faux fur on a human arm — they’re living, breathing creatures. “There’s a real alchemy with puppets. It’s like magic,” Sesame Street head writer and puppeteer Joey Mazzarino tells EW. “You put it on, it comes to life, and you lose the thing behind it, whether it’s me or one of the other puppeteers.” Grey’s Anatomy actor Jesse Williams felt that same alchemy when he filmed a guest appearance on Sesame Street. Williams appears on Thursday’s episode, teaching viewers about the word “furious” alongside Elmo and a fly named Felix. Though Williams had never acted with puppets before, it didn’t take long for him to adjust. “I think about Elmo as a person,” he tells EW. “Once the camera’s rolling, it’s Elmo, and Elmo’s riffing. He’s alive, we’re both ad-libbing and making it work.” Growing up, Williams watched Sesame Street with his two brothers, and he recalls being a fan of Bert and Ernie, Grover, and Big Bird. Though Elmo joined Sesame Street later in Williams’ childhood, he was still thrilled to learn that he’d be appearing alongside the red guy. “I was excited because Elmo is a slick character,” Williams says. “A lot of smart, under-the-breath humor. Very witty, very fast, which is an ideal scene partner. So I was excited, and I knew that it would be fun and that it would be spontaneous and we’d get to riff a bit and improv a little bit.” Check out Williams’ “Word on the Street” segment below: After shooting the segment, Willams took Felix’s furious grievances to heart when the on-set photographer snapped a few pictures of Williams, Elmo, and Felix (puppeteered by Eric Jacobson, who also is the man behind Grover). When the photographer gave the direction, “Fly, move a little to your right,” Williams was quick to correct him: “It’s ‘Felix,’ not ‘Fly.'” Williams’ guest appearance is in the episode titled “Leela’s Cell Phone Addiction,” which airs on Thursday, Oct. 17 on PBS at 10 a.m. ET/PT.