The squeaky performance came after Ross tasked the pop star with inhaling a balloon full of helium before singing a popular song.
Spears choose Swift's hit single off her latest album 1989, briefly singing the song's chorus before laughing.
Also during her appearance on the British talkshow, Spears opened up about her dating life explaining how she's perfectly happy being single.
"A lot of men are about games," the 34-year-old stated. "It's just the mind game with guys, the calling back and texting, it's just too much, it's silly. Actually, I'm not looking for men right now, I'm really happy with myself. I'm not looking for anything, I'm fine with the way I am."
"I like someone that's just nice overall, just a nice guy really is groundbreaking in this world," she continued about what type of men she's interested in.