Partners for a decade, Rapp’s bag men are an odd couple, Burris an agitated swaggerer given to flights of vocabulary, the older Dantly a sadsack who is shedding his memory like hair. Burris is in continual motion, bouncing from air karate to push-ups abetted by a little blue-plastic exercise aid. Dantly just lies on the bed, his bare feet sticking up like pink periscopes. “Fuckin’ Zanich!”, explodes Burris of the pair’s employer, recalling the immortal entrance of Teach in David Mamet’s American Buffalo. Dantly, on the other hand, seems to be imploding; a man in existential crisis, he has developed a penchant for shoving things down his pants (most recently an ice scraper, with tender results) because it makes him feel he’s getting away with something. Rapp, whose powerful Nocturne was primarily a monologue, makes amusing hay of the dialogue between these two, with Burris slamming muscular semantic riffs across the net, only to have Dantly ping some deadpan non sequitur sideways off the court. But whereas Nocturne, which the ART presented last fall, spun gold from its lyrical yet visceral language, Animals and Plants is too derivative to make the most of its own considerable linguistic chops.

This is not to say the play is without merit — and who would have guessed from Nocturne, which traces the painful journey of a young man who inadvertently kills his sister, that Rapp had comedy, as well as such potent grief, in him? Neither is Animals and Plants without aching undercurrents, primarily in the character of Dantly, whose alienation from himself takes both comic and poetic form. “I shaved my ass today,” he announces casually, signaling yet another attempt to change, to molt, to transform into some new stage of himself. Later, touchingly, he malaprops that though he knows himself to be “biographically human,” he feels more like a fern or a cactus. And in the play’s loony yet poetic final image, he sets out to plant himself where neither fauna nor flora can survive.

After intermission, Rapp brings on a woman, a ditsy but apparently psychic chick that the two men met in a local head shop. Burris has disappeared, ostensibly to look for a snow shovel, and Dantly awakes to the perkily ingratiating (if obviously named) Cassandra, in bare midriff and sheepskin coat. For my money, the exchange between these two lost souls goes on too long, though there are good things in it, among them a sweetly off-kilter rendition of a song from a Rudolph the Reindeer TV special. And though I’m willing to forgive Rapp’s breaking of Chekhov’s rule regarding the introduction of weapons that aren’t to be used, on the grounds that metaphor beats melodrama any day, Animals and Plants could do without the never-built-upon mysterious phone calls.

But Rapp is a formidable talent, and he works his own obsession with language into the dynamic of Animals and Plants. Burris is something of a linguistic showoff; as Dantly puts it, he uses words for his own “recreational boner.” It’s when, for the first time, Dantly fails to take Burris’s word for it about words that the fabric of their surrogate-familial bond starts to fray, making way for the betrayal that rips it utterly. And in frequent Mamet collaborator Scott Zigler’s energetic production, Evett hurls phonemes like a thug on amphetamines while LeBow’s language-deficient character languishes like a limp dick. The irony is that, puzzling over everything from the meaning of “lanyard” to where he fits in the “Divine Order of Things,” Dantly seeks self-definition in a thinner but more searching dictionary.

At the Hasty Pudding Theatre, ricocheting and sagging respectively about J. Michael Griggs’s busily tacky set, Benjamin Evett and Will LeBow bring Rapp’s play to crackling life. Evett goes for broke as the more volatile Burris while LeBow delivers a performance that’s as heartbreaking as it is hilariously matter-of-fact. The crazed ape-communication demonstration with which his Dantly greets the knowledge that his only human connection has snapped is ludicrous yet almost frightening. And ART Institute student Frances Chewning hits the right notes, too, as the bubblegum prophetess who tries to comfort Dantly by cheerfully comparing him to pancakes. Goodness knows, there’s more to savor here than flapjacks. But you can’t help wishing Rapp hadn’t borrowed the plate.