UFC 206 may still feel like it's lacking a big standout title fight, but one fight on the undercard has been nicely simmering away over the past few weeks.Doo Ho Choi versus Cub Swanson might not be a fight that gets the bulk of the media attention leading into the event on December 10, but should things continue the way they have been, we could have a nicely heated up rivalry between the pair.The rivalry began back in August when Choi appeared on Korean TV and politely challenged the UFC veteran. Swanson responded shortly after and told the UFC he'd happily take the fight. The date was then booked for December 10 in Toronto, Canada, at UFC 206, and since then a verbal warfare has broken out in the media.Just last week, Swanson told FloCombat Choi would soon realize he'd made a big mistake challenging him."He must think I don't have it anymore," Swanson said. "That I've lost a step. Well let's see on fight week when he has to actually look me in my eyes...and he sees no fear or doubt...because I've already been fighting the best of the best. He'll realize then that he's fighting a killer."Having obviously been made aware of that interview, a few days later Choi returned fire via the Korean press, and he had his own warning for Swanson."Considering his position, he should feel less comfortable about this matchup, because it's me of all fighters," Choi told SPOTV . "He already fought top-rank opponents, and he's not in a position to fight them again. This fight against me will irritate him a lot. Now he has to fight with [low-rank] fighters, and he unfortunately picked the most difficult opponent he could in this group."Choi believes the American has lost his killer edge and that his past few fights haven't been impressive."He had a three-fight winning streak of knockouts in 2012," Choi said. "Since then, you can see in his recent fights that he no longer has that killer instinct. Against Hacran Dias and Tatsuya Kawajiri, he only managed to win by close decisions. If it were me, I would have knocked them out.[instagram url="https://www.instagram.com/p/BLlaQUmgAOK/" hide_caption="0"]"If he watches my recent fights, he would notice who the real 'killer' here is. I would say Swanson is more of a 'veteran' than a 'killer' these days."The South-Korean then said he welcomed Swanson's aggression and challenged him to stand toe-to-toe with him in Toronto."Just like he said, I also expect him to be aggressive and try and finish the fight," Choi said. "He's more than welcome to try do that. My aim always is to finish my opponent, and I will enjoy going head-to-head. Let's see who is going to be the last man standing in the Octagon."