If a character accepts the challenge, move them into base contact with the challenger – after all, what good is the narrative of a challenge without the visual reality? If, for whatever reason, this is not possible, assume that the two models are in base contact (this might require a little gumption to work out, so it's best to move the model if you can). These two characters must direct all of their attacks (except Breath Weapons, Impact Hits and Stomps – these are directed at the unit as normal) against each other – they cannot be attacked by any other model for that round of close combat. However, note that they may still be affected various special rules and abilities that normally affect models in base contact.