In a new online segment for The Tonight Show, the duo created songs 'on the spot' based on titles submitted by fans.

The first title pulled from the fishbowl was Witness The Fitness, which they made into a rock workout song. The second, Quickly Clicky Pens, started as an acapella jam when Niall started rocking the harmonica. A highlight is Horan and Fallon's harmonizing during the last song, Stepping On Toes.

Watch the improv hilarity ensue below:

 

 

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