There is one joyous moment in the Fabric Workshop and Museum's current exhibition, "Ally," and it is about someone else's joy.

It is a video, projected on a very large screen, showing the face of dancer-choreographer Anna Halprin as she watches a performance of Rope Dance, a work she created for this exhibition, in collaboration with sculptor Janine Antoni and choreographer Stephen Petronio. Halprin, who is 95, has a deeply lined face, and as she reacts to the dance, you can see where every wrinkle came from - some to express surprise, others to show concern, curiosity, amusement, elation, pride, and a flow of other emotions. It is a lived-in face that is still vehemently alive. You can believe this moving portrait was made by a sculptor.

One thing few people will be able to see is the dance, in which a group of people holding ropes spontaneously form a network that emboldens them to lean and gesture. This description makes it seem suspiciously like a corporate team-building exercise, but at the press preview, it produced moments of surprise and delight, even beauty. It will be performed three more times between now and July 31 for small groups of participants who have already reserved online.

For the purposes of "Ally," though, Rope Dance is all about Halprin's response, not the dance itself. The exhibition is organized around four performances by the three artists in various collaborations. But the exhibition is focused not on the performances, but on what is left behind. As the museum description says, "Together, the artists ask: How might the ethereal forces of performance be encountered in the exhibition space where objects have long reigned? . . . Each work reconfigures the relationship between a dance and its means of residing in a gallery."

"Ally," which grew out of a residency by Antoni at the Fabric Workshop and Museum, is an ambitious undertaking that received substantial philanthropic support from Pew and others. More than 100 people were involved in some way or other in making it happen. The artists say they found the experience exhilarating. And the preview I attended, which included three performances, was memorable and sometimes thrilling.

Still, isn't there something perverse in inviting a museum audience to see only the relics of an artistic process? Or perhaps the question is really a cynical one: What can be shown or sold after a performance is over?

Consider Paper Dance, conceived by Halprin and Antoni and performed by Antoni. It consists essentially of the artist writhing around on the floor, at times naked, with a huge roll of brown paper. Through actions both violent and subtle, she makes the paper take on an ever-changing range of shapes. The paper shifts from being a vast landscape to being a flowing gown in an instant.

We can see it as a sculptor's reverie, as she uses her hands and body to form and reform the paper to embody outbursts of energy. Antoni inhabits the paper and brings it to life.

Once she is finished, though, there is just a big pile of crumpled, ripped, and folded paper left at one end of the gallery, where it joins the paper from past performances. You can call it art if you want, but it really looks like garbage. At the other end of the room are pristine rolls of paper, each a promise of a future performance. (She will perform weekly throughout the run of the show.)

The audience sits on packing crates that hold Antoni's works. She unpacks one and repacks one during each performance, so only one work at a time is on display. She is very careful that there should not be too much to see.

Swallow is an installation that memorializes a performance, of sorts, that happened only once, in November. Antoni and Petronio each swallowed one end of a narrow, 10-foot-long piece of cloth woven at the Fabric Workshop and Museum. As they swallowed the cloth, they were brought closer and closer together until they were touching. Then they regurgitated the cloth. Ten witnesses watched, including an expert on swallowing disorders, young twins, a poet, a lawyer, and a subway worker.

A single photograph was made of the event, screen-printed in graphite and saliva on a piece of cloth. This is shown in a vitrine, where it is being consumed by moths. The testimony of the witnesses to the event - some of it contradictory - is piped through speakers to pairs of wooden chairs, joined at the corners, much as the artists briefly were.

And at the end of the room is a platform on which is displayed a gold reliquary that holds the remains of the swallowed fabric. The reliquary mimics some of the shapes of the larynx and esophagus and is topped with a two-chambered blown-glass vessel evoking the artists' mouths, where the cloth is rolled. There is also a magnifying lens at the top so viewers can look down and see the spot where the swallowers converged.

I suspect many visitors to the exhibition will wish they could see the dance performances, but most will be grateful to be spared witnessing this borderline-disgusting event. Even listening to the witnesses' accounts can get a bit intense.

This is, of course, a work of religious art, created to impress those who experience it with the gravity and power of an event they have not seen. Though the work evokes Catholic forms, the religion here is the religion of art, and artists are its priests, or perhaps its gods. This art is performed for the artists' sake, and communicated only indirectly to the public.

"Ally" reminds us that religions have found ways to evoke and make meaningful events whose reality congregants must simply accept on faith. But it also reconceives art as an esoteric process whose mysteries are available to only the few.

When we go to a museum, we don't want to see secondhand evidence of art. We need to see and experience the thing itself.