Often during a song, some singers with almost no air in their voices, sort of roll on their o's, switching from one note to another without a break. Listen to the video below on 0:11. How can I possibly manage that?
YouTube Video: Highasakite - Leaving No Traces (Live from Rockefeller, Oslo).
Another example is what she is doing here, at 4:02. Instead of just switching note, she rolls over from one note to the other. She often does it when she’s making an ‘O’- sound.