Key and Dana were guest stars on the September 18 installment of MBC's 'Radio Star.'  On this day, the two talked about their kiss scene in the musical 'Bonnie & Clyde.'

It was revealed that Dana felt awkward about the kiss because the two of them were very close.  Key then said something shocking: "We made a rule that we would not use our tongues."

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Kyuhyun asked who made up that rule.  Key pointed to Dana and Dana yelled, "You did!" She quickly became a victim of Key's teasing as she tried to convince everyone that Key was the one who made up the rule.  Kim Gu Ra sided with her, half-jokingly saying that Key was a scary person for bending the truth.  

Key also said that during their practice that day, Dana started using her lips more, which Dana denied.  She protested, "Key wanted me to," and related a time Key asked her, "Why do you dislike kissing me so much?"

To support their personal claims in this amusing argument, the two even resorted to mimicking their kissing with their hands.  Watch the full clip above to see for yourself.