On Saturday, MoMA attendees watch Tilda Swinton sleep in her performance piece The Maybe.

The surprise star of the opening weekend of New Directors/New Films was none other than Tilda Swinton. And today, she's back for an encore performance at MoMA.

An unexpected bonus attraction of the annual festival—a showcase for emerging filmmakers co-presented by Film Society and MoMA—features the Oscar-winning actress sleeping in a raised, glass-enclosed twin bed. She appeared to sleep throughout the day on Saturday, apparently undisturbed by visitors and some ND/NF attendees who made their way to and from screenings downstairs at the museum. Today she is back at MoMA sleeping in a different part of the museum.

Swinton surprised attendees by staging the pop-up performance, The Maybe, inside MoMA's atrium unannounced on Saturday. It was the New York debut of a work that she originally performed at Serpentine Gallery in London back in 1995. The following year she took the piece to the Museo Barracco in Rome. She'll continue presenting the piece on various days through November. 

Twitter lit up with talk of Tilda Swinton's MoMA appearance on Saturday morning once attendees realized it was indeed the actress. Museum officials watching Swinton sleep on Saturday afternoon near the exhibit said that her appearances would not be promoted or announced in any fashion. Some visitors snuck camera phone photos of the sleeping actress even as security guards waved away the cameras.

Introducing a screening on Saturday, senior MoMA curator Raj Roy advised ND/NF attendees that Swinton was presenting The Maybe just up the escalator from MoMA's movie theaters. By the end of the day, large crowds had gathered for an up close opportunity to gawk at the star.

Today, Swinton is sleeping in an upstairs gallery in a different part of the museum. While she's harder to find, she's drawing large crowds to room with video installations by a Scottish artist.

The Maybe features a reclining Swinton, wearing loose clothing, throughout the entirety of MoMA's operating hours. She's resting with her head on a pillow, her eyes closed and glasses placed nearby. An untouched pitcher of water is at the corner of her bed. A few times, viewers detected a twitch from Tilda, while those who stayed longer saw her switch sleeping positions or move her arm.

Tilda Swinton at MoMA on Saturday. Image via Gothamist

Standing near the sleeping Swinton, MoMA curator Klaus Biesenbach watched as victors marveled at the actress. Some moved in really close to examine Swinton. Hanging back, Biesenbach—seen in the recent documentary Marina Abramovic: The Artist Is Present, about the wildly popular show he curated three years ago—said the the piece is best viewed from a distance of just one foot. Tired after a long night of preparations for the piece's debut, Biesenbach spent much of the afternoon watching attendees watch Swinton sleep.

Guests seemed bemused and bewildered by Swinton and her piece. Some seemed to stick around for hours to stare, while others seemed unfamiliar with the famous actress.

As closing time approached on Saturday, a few famous friends arrived at the museum. Michael Stipe circled Swinton's bed and then went upstairs to view the piece from a distance (a museum guard stopped him from snapping a photo) and then James Franco showed up to check out the scene. Guards ushered guests away as the clock struck 5:30PM, but the bold-faced names stuck around, presumably to welcome Tilda Swinton from her slumber once the museum was empty.

“An integral part of The Maybe's incarnation at MoMA in 2013 is that there is no published schedule for its appearance, no artist's statement released, no museum statement beyond this brief context or image issued. Those who find it chance upon it for themselves, live and in real—or shared—time: now we see it, now we don't.

The actress will appear at MoMA — unannounced — seven or eight more times this year.