TALK about tall, dark and silent. Better yet, don’t, because that would interrupt Stephen Rea’s intense concentration on the computer-screen footage he’s watching of Buster Keaton and Charlie Chaplin in “Limelight.”

The delight that occasionally cracks the close concentration of Mr. Rea’s long, gentle face does a kind of synchronized and symbiotic jig with laughter coming from the other quiet man at the rehearsal table on the second floor of the Public Theater, Sam Shepard.

Mr. Shepard is the writer and director of “Kicking a Dead Horse,” the new play starring Mr. Rea that begins previews Wednesday. The two men hoot at the same pratfalls and comic disasters in the movie. They remember the same bit players from old Hollywood. Their faces both swing to attention when a young actress, Elissa Piszel, enters the room. Her role, ghostly and funny at the same time, is brief and nonspeaking and calls for her to wear a see-through slip in the play, about a man lost in the American West with no plan and a dead horse. To prepare for the production Mr. Rea, 61, and Mr. Shepard, 64, were deconstructing the film’s famous duet, in which the violin-playing Chaplin eventually tumbles off the stage.

Mr. Shepard’s work has almost always centered on twosomes. Fathers and sons, husbands and wives, lovers, brothers, even-numbered families, humor and grief, violence and contemplation locked in mortal combat. But in this play the Other that the protagonist debates is himself (and the equine carcass he’s trying to bury). His dilemmas flow from the search for authenticity and the roots of American global perfidy that has brought him, a New York dealer in expensive Western art, to his past’s terrain.

“It’s a massive thing,” Mr. Rea said earlier of the single-character play. “It’s like ‘King Lear,’ except you have to play the Fool as well.”

That there’s a bit of “Hamlet” in the grave digging struck him as intriguing. “And Beckett, of course, an influence on both of us,” he added. Mr. Shepard had mentioned J. M. Synge’s corpse-happy “Playboy of the Western World” when he discussed the premier of “Dead Horse” at the Abbey Theater in Dublin last spring, with Mr. Rea as its Irish star.

Until recently Mr. Rea dismissed much of the theater being done in Ireland as moribund, the Abbey in particular, and he had left the stage to make movies almost full time. In August he returns to Ireland to shoot “Ondine” for his frequent director, Neil Jordan.

But that embargo seems to be changing. Mr. Shepard first wrote a play with Mr. Rea in mind, “Geography of a Horse Dreamer,” in 1974, and he wrote “Kicking a Dead Horse” for him (it’s dedicated it to Mr. Rea too), as well as his next one, “Ages of the Moon,” scheduled next year at the Abbey. That theater, reinvigorated over the past three years by a new artistic director, Fiach Mac Conghail, now has a steady working relationship with Mr. Shepard.

“Stephen is the kind of actor you can hang a whole character around,” Mr. Jordan said. “That’s why he’s been directed by Beckett and Harold Pinter and Sam Shepard.”

For “Kicking a Dead Horse” Mr. Rea also has to tangle with the physical intricacies of roping (and being roped in by) a dead horse, and Mr. Shepard brought in Bill Irwin the other day to teach him some tricks.

“On a very coarse level it’s a clown show,” Mr. Shepard explained.

Oskar Eustis, the Public’s artistic director, suggested that Mr. Rea had mastered Mr. Shepard’s material “because he has this distinctive quality as an actor of being simultaneously exquisite with poetic language and able to play the common man.”

That the quintessential Irish actor is collaborating with the quintessential cowboy mouthpiece is not so much incongruous as crucial, Mr. Eustis said, “because Stephen’s otherness helps strike the existential tone.”

Dismissing any fancy analysis, Mr. Shepard said: “There’s no one thing in Stephen’s performance that makes him a brilliant actor. It’s more that he’s an extraordinary man who grew up in Belfast during all the horrible stuff the Irish refer to as the Troubles. He’s been through a lot, and it shows on his face.”

Mr. Rea was born Protestant in Northern Ireland, the son of a bus driver, attending working-class schools until he made it to Queen’s University Belfast.

“The thing you feel about growing up in Ireland is that you wish you hadn’t had to deal with all the stupidity and absurdity of a sectarian society,” he said. “It’s vile and repulsive.”

Increasingly political, in 1980 he founded the Field Day Theater Company in Derry with Brian Friel to make art that might create greater understanding among their country’s warring factions. He also married Dolours Price, an I.R.A. member who had served eight years of a life sentence for a bombing. (They divorced in 2003.)

Looking back over Irish history, he said, he sees more and more that reminds him of the American attitudes that Mr. Shepard uses for target practice in “Kicking a Dead Horse,” and similarities between the American West and the western part of Northern Ireland, where Field Day was based.

“The English conquest of Ireland was the prototype for the American conquest,” he said, “the modern version of which is Iraq. The original Gaelic civilization got pushed further and further west, like the Native Americans.”

Mr. Shepard, who still mines his part-Irish ancestry with his Appalachian-music band the Holy Modal Rounders, might be interested that Mr. Rea’s father once contemplated emigrating to the United States. “Sam’s work makes a lot of sense to me,” Mr. Rea said.