One of the few thoroughly likable characters in the Coen brothers’ quirky new folk-era film “Inside Llewyn Davis” is a striped tabby cat whose natural curiosity sets key parts of the narrative in motion.

“The film doesn’t really have a plot,” Joel Coen said during a Cannes Film Festival press conference this spring, as reported by the London Telegraph. “That concerned us at one point; that’s why we threw the cat in.”

Oscar Isaac plays the title character, a borderline amoral singer scratching out a living on the early 1960s coffee shop circuit. John Goodman plays Roland Turner, a drug-addled jazz performer who shares a car ride from New York to Chicago with the brooding Johnny Five (Garrett Hedlund) at the wheel and Llewyn and the cat riding shotgun.

“Every time I’ve seen it, I’ve had a different reaction to it,” Goodman said of the film, also starring Carey Mulligan, F. Murray Abraham, Justin Timberlake, Robin Bartlett, Ethan Phillips, Stark Sands, Adam Driver and Jeanine Serralles. “You could really do short stories about all the characters. All the people were so richly drawn.”

Goodman’s character spends his time alternately snoozing and sermonizing, pontificating thunderously from the back seat as the unlikely trio (quartet?) roars west.

“I had a lot of long speeches. I started hearing a voice,” Goodman said during an interview with The Atlanta Journal-Constitution, discussing his method of getting into character. “It was happening organically. I learned to trust the process as it happened.”

“Inside Llewyn Davis,” which opens in Atlanta on Dec. 20, is the latest Coen project to feature Goodman; he also appeared in “O Brother, Where Art Thou?,” “Barton Fink” and “Raising Arizona,” among others.

Goodman also has kept busy in Atlanta’s ever-growing filming scene, with roles in “Trouble With the Curve,” a baseball-themed movie with Clint Eastwood, Amy Adams and his “Llewyn” co-star Timberlake; “Flight,” the drama for which Denzel Washington earned an Oscar nomination; and “The Internship,” a comedy starring Owen Wilson and Vince Vaughn.

“The film industry’s hopping down there,” he said.

Goodman was excited to collaborate with the Coens again and intrigued by his memorable yet sparsely drawn character, who blows in and out of the movie like a storm cloud.

“It makes the audience wonder about it on their way home,” he said of the unorthodox project. “You flesh it out for yourself.”

So what of his furry co-star?

“I only had to deal with the cat once,” he chuckled. “He was a well-behaved cat. He was a good kitty.”