Cardi B left U.S. talk show host Jimmy Fallon lost for words after explaining the unexpected meaning behind a line in her new single Up.

The WAP hitmaker is known for her raunchy lyrics, but she caught comedian Fallon off-guard on Thursday as she revealed one part of the song originally referred to an uncomfortable constipation situation. The line in question, which she had borrowed from her husband, Migos rapper Offset, is: "If it's up, then it's stuck".

During The Tonight Show Starring Jimmy Fallon interview, Cardi admitted she initially thought it was a "Georgia thing" as Offset, who is from the state, says it "a lot", but she soon learned fans from other Southern U.S. states are also familiar with the phrase, so she was inspired to use it too.

"Um, so have you ever taken a poop, right, and it don't come out?" Cardi began to explain, as the stunned funnyman looked down at his desk.

"It's just up and it's stuck. Yeah," she shared.

After an awkward silence, Fallon uttered, "Wow," while Cardi simply nodded.

"I mean, I guess you can take from it whatever you want. There's other ways to look at it, I guess," Fallon reasoned, as Cardi agreed, "It's a metaphorical quote."