Season nine, feeling fine and it's time to rhyme this line!

How I Met Your Mother is taking things one step further beyond a musical number by airing an entire episode told only with rhymes!

"We just shot an episode where the entire thing is in rhyme. And it was so much fun," Cobie Smulders tell us exclusively. "It's like every second line is a rhyme. It varies; you gotta watch it!"

Sounds like quite the challenge for the writing staff. But for a group of people who managed to turn a mother mystery into a storyline that's lasted nine seasons, this was probably a cinch.