Okay, there's been a great amount of fanwhinge over the whole Vulcans Can't Lie concept, which has been so irregular throughout all the series and movies that it's impossible to know whether Vulcans physically cannot lie or if they just think it's illogical ever to do it. Spock, Tuvok, and Kim Cattrall have all gotten away with the whole "I wasn't lying, I was being creative with the truth," thing while there have been other occasions where it's mentioned -- not necessarily by Vulcans -- that Vulcans "can't" lie. In this particular case, I'd argue that Mestral's lying came about because he's showing obvious signs of being a lapsed Vulcan -- the excessive interest in humans, his constant interaction with and defense of the humans, potentially becoming emotionally involved with one of them -- and is just getting lazy with Vulcan practices as a result. Now, before I decide to write my thesis on this instead of on the wines of the greater Spitgully region of Yemen, back to the snark!