A strange object spotted in the sky over Chicago has left both aviation and UFO experts baffled.

The “weird black object” was captured on video by a resident named Alvana, who witnessed the mysterious phenomenon from the roof of her home. “I literally have no idea what it was,” she says. “There is nothing comparable. It was a ball of some sort with two long strings or belts hanging from it.

I felt total confusion and a bit creeped out.” Alvana goes on to say the object floated slowly across the sky, traveling “a few miles in about 20 minutes” before it eventually disappeared.

Alvana says she brought the footage to aviation experts and UFO watchers, but neither could provide her with answers as to the strange object’s origin.

While some online commenters suggested it might have been a weather balloon, several refuted the claim, with one writing, “I’ve never seen a balloon just hang still in the open air like that. It should bob, even if just a little.”