WHITINSVILLE — “Sylvia” is one-of-a-kind — a theatrical chew toy that dog lovers are sure to relate to, while theater lovers of all persuasions are invited to nibble gleefully at A.R. Gurney’s decidedly unusual domestic triangle.

There was plenty to bark approvingly about in director Matt Carr’s smartly staged and expertly acted Pilgrim Soul Production on Friday night. “Sylvia” may not be your typical love story, but Ellen Elsasser’s lovably obsequious performance in the title role of a part-Lab, part-poodle burrowing her wet little nose into the lives of a middle-aged couple goes a long way toward blurring the distinction between canine and human.

Picked up in a park and brought home by Greg (Todd Darling), a midlife crisis candidate anxious to fill the void in his life caused by a dreary job and argumentative boss, Sylvia’s a charmer from the get-go. She paws her way into Greg’s heart with irresistible adoration.

Given the human attribute of speech through the eyes of Greg and his wife, Kate (Betty Kristan), Sylvia comes across as a creature full of primal wit and biological urge that, thanks to Elsasser’s marvelous verbal calibration and physical invention, is often hilarious to behold.

When Greg takes her for a walk in the park and meets a fellow dog owner, Tom (Erik Evan Johnsen), Sylvia can’t wait to have a romp with Tom’s studly Bowser. What’s both funny and disturbing about the scene is how jealous Greg becomes over Sylvia’s need to scratch that panting itch, until Tom reminds him she’s only a dog.

Kate invidiously views Sylvia as a threat to her marriage, now that the kids are on their own. She and Greg can finally have time to themselves again, and the last thing Kate wants is another “child” in her life, one who defiantly remains sitting on the couch when Kate tells her to get off.

Yet the friction between them never really rises to the level of serious antagonism, and what is particularly good about Kristan’s thoroughly nuanced performance is that we can understand where Kate is coming from. She has every right to want the love and attention from Greg that Sylvia has usurped. As endearing as Sylvia may be, Kate has her needs, too, both personal and professional, and Kristan realistically portrays Kate’s unhappy frustration.

We can commiserate with Kate as perceiving Greg and Sylvia’s bonding as some sort of strange “fling,” one she tries to undermine by teaching Shakespeare overseas, confining Sylvia to a 6-month quarantine.

But we can also side with Greg for embracing Sylvia as an object of rescue.

Darling, for his part, does a terrific job of dealing with the two “women” in his life, the strain of emotional conflict limpidly drawn across his face and heard in his placating voice. He loves his wife and he loves his dog, and he’s having a tough time reconciling the two.

It’s a crazy triangle wonderfully acted by all three and resolved with surprise and poignancy.