And not regret it, for the liver that you have,
Is just impossible

The story:

I believed those were the actual words for a long time, and sang along with Perry using those words often. When some of my family members told me those couldn't be the correct lyrics, I let them hear the recording. They were convinced I was right. Finally though, I looked the words up online, and sure enough I was wrong. Still, when I hear the song, to this day, I don't hear anything but "for the liver that you have."