When Jeff Koons and Lady Gaga began collaborating on the cover of her 2013 album Artpop, “she wanted to get naked,” Koons recalled Wednesday night during a talk at the FLAG Art Foundationin New York. “She basically wanted to make ‘Made in Heaven,”’ he said, referring to his 1989 series of paintings showing him and his ex-wife, pornstar Ilona Staller, having sex. (Instead, the pair referenced his more recent “Gazing Ball” series, with Gaga straddling one of the artist’s signature blue reflective orbs.)

Sex was the subject of much of the event, hosted by collector Glenn Fuhrman in honor of the current show at FLAG, which features work by Koons, Cecily Brown, and Charles Ray, through May 14.

Koons went on to reminisce about his unrealized dream of dangling a vintage steam engine from a 166-foot-tall crane.

“I would love to see it be built. It almost got built” at the High Line, he said, but “one of the tenants in one of the buildings wasn’t really for the piece.” The dangling train, which he estimated would cost between $25 million and $50 million, “would perform multiple times a day. It would start to do everything a real train does. It takes eight hours for it to build up enough energy to leave the station, but this would be sped up” into about 20 minutes. Then the light might flicker on, the engine would rev up and “you’d start to hear a ‘ding ding,’ and all of a sudden a first kind of pump of steam, like ‘chooo,’ like a piston firing. And that’s a metaphor for people, which are breathing machines, and this engine is just in the air and then just continues to build momentum until about three minutes in it would be going full speed, which is about 80 miles per hour. Then it would be ‘woo woo, woo woo, woo woo,’ this kind of orgasmic climax.”

Koons also offered a bit of insight into his legendary salesmanship skills with a story about his first job in New York, as a ticket-taker at the Museum of Modern Art. On staff breaks he’d sometimes help man the membership desk, where he quickly noticed how rarely anyone sold them. He took the task upon himself, and “over a period of about two years I doubled the Museum of Modern Art’s membership,” he said proudly.

But then it was back to “Made in Heaven,” with a recollection of a day he and his young children visited a gallery of his work. “They look at the Pink Panther and say, ‘There’s the Pink Panther!’”

“And then, ‘There’s the rabbit!’”

“And then, ‘There’s Ilona’s asshole’ and they go—” the words were drowned out by laughter from the crowd. “They automatically understood and valued the work. It’s a dialogue that’s just about biology, one form of the eternal,” he said. Of course they understood that.