Even the best actors sometimes find it hard to hide their true feelings onstage. It’s particularly difficult when the character’s nemesis is a cuddly orange tabby and he’s purring like crazy.

“I have to not like this cat,” actor Chris Dinolfo said during a recent rehearsal of Constellation Theatre Company’s production of “The Lieutenant of Inishmore,” Martin McDonagh’s pitch-black comedy set against the backdrop of the conflict in Northern Ireland. But it wasn’t easy for Dinolfo to hide his affection. The cute tabby, named OJ, was content as could be in his arms, happily flicking his tail, all while Dinolfo’s character, Davey, was lobbing curse words at him.

Grumpy cat: Thomas Keegan playing Padraic in "The Lieutenant of Inishmore" lifts OJ (Orange Juice) during a dress rehearsal. (Photo by Kate Patterson for The Washington Post) (Kate Patterson/For The Washington Post)

This is the first acting gig for OJ, who belongs to assistant stage manager Sarah Kate Patterson. And he isn’t the only feline in the production. There’s also Mousse, a black longhair that Patterson adopted from the Washington Humane Society specifically for the show. (There will be an adoption event after the Sunday matinee.) For the violent, gory scenes involving the cats, the company is using stunt-double puppets, partially concealed by baskets and other objects to maintain the illusion of a real cat. This allows the actors to focus their venom on the inanimate objects.

“I’ve said from the outset, ‘Hate the cat in your basket, love the cat in your arms,’ ” director Matt Wilson said. “When the role of the cat is being played by a puppet, we can yell, scream or do all kinds of violence, but when you pick the cat up and hold the cat, you have to find some love for the cat.”

Most cats are not well-suited to the theater, according to famed Broadway animal handler Bill Berloni (dogs and even pigs are easier to work with). Cats are not eager to please and are easily startled by loud noises, such as shouting and gunshots, which are regular occurrences in this play. In fact, many companies that stage “Inishmore” don’t bother with real cats, finding it easier to use puppets the entire show.

A close up of Mousse, one of the two cat stars appearing in "The Lieutenant of Inishmore." (Photo by Kate Patterson for The Washington Post) (Kate Patterson/For The Washington Post)

Although Wilson had never directed a show with live animals, he decided to use OJ and Mousse in “Inishmore” because real cats, he said, “further plunge us into seeing the truth of reality.” But that’s not to say it hasn’t been without challenges.

“I think it is impossible to direct a cat,” he said. “I think it is possible to direct actors and props designers and scenic designers so they make choices that rein in the possible choices that the cat can make. It’s about: When do we pick the cat up, when do we put the cat down, when do we just take the cat away?”

The actors, who are used to taking their cues from a director, now also have to heed the direction of Mousse and OJ.

“We’ve been clear about, sort of, in an ideal world, this is where the cat comes in and goes out,” Wilson said. “But then at any point, we honor what the cat is doing now and wants to do now. There are alternate blockings already in place [if] the cat doesn’t want to be held.”

If it seems as if the cats are the stars of the show, well, in a way they are. An old theatrical adage, commonly attributed to W.C. Fields, cautions, “Never work with children or animals” because they’re bound to steal whatever scenes they’re in.

“It requires a higher clarity of storytelling,” Wilson said. “When the cat is there, we’re watching the cat and not paying attention to anyone else. Which, also, I think is the same as the firearms in the show. As soon as the gun comes out, it becomes about the gun. We don’t ever want to be in a place where the dialogue of the show has to compete with a cat or a gun.”

Mark Lee Adams, who plays Donny in "The Lieutenant of Inishmore" left, takes a break with Chris Dinolfo, who plays Davey, and cats OJ and Mousse (Photo by Kate Patterson for The Washington Post) (Kate Patterson/For The Washington Post)

Both Mousse and OJ seem to be thriving in their unexpected careers. Their pre-rehearsal ritual involves eating a bowl of cat food, sniffing around the stage for 10 minutes and then curling up on chairs to nap until they’re called. Only once during a recent rehearsal, when Dinolfo and co-star Mark Lee Adams had to pull OJ out of a basket and hand him off, did the cat get a bit panicky.

“In that respect, the cats are like other actors,” Wilson said. “Sometimes they make different choices, and the scene partners have to adapt.”

If you go:
The Lieutenant of Inishmore

By Constellation Theatre Company at the Source, 1835 14th St. NW.
202-204-7741. www.constellationtheatre.org.

Dates: Through March 8.

Prices: $20-$45.