Lady Gaga put her Rain On Me duet partner Ariana Grande on the spot by asking her to sing, while she performed an interpretive dance in front of her.
The Poker Face star admits her new pal had no idea what to expect when Gaga asked her to join her in the studio - and she really tested her.
"I think maybe she assumed that it'd be that she came in and I was like, 'Here, just sing this and thank you so much for your time,'" Gaga tells Apple Music's Zane Lowe, "but instead I asked her what she needed, how she wanted to do things...
"I said to her, 'OK, now everything that you care about while you sing, I want you to forget it and just sing. And by the way, while you're doing that, I'm going to dance in front of you', because we had this huge big window...
"She was like, 'Oh my God. Oh my God. I can't. I can't. I don't know. Oh my God. OK, OK'. And then I did it and she sang, and she started to do things with her voice that was different. And it was the joy of two artists going, 'I see you...' We create things that make us feel comfortable. We put them all around. I do it all the time. We all do things to make ourselves feel safe.
"I always challenge artists when I work with them. I go, 'Make it unsafe, make it super f**king unsafe and then do it again'. And it was just awesome to watch her."
During the interview with Lowe, Gaga also heaped praise on Billie Eilish, revealing she sent her flowers after one awards show where the Bad Guy singer piled up the wins.
"There was one night where she just swept a whole bunch of awards and I said, 'Send her some flowers'. I wrote her a note and, for me, it's healing, because I go, 'You know what? That hurt me that I didn't get that, but that's OK, because I'm going to be that for someone else'. And me being that for anyone is also a gift for me."