Since his debut feature, Primer, hit theaters eight years ago, Shane Carruth has been a quiet presence in the world of cinema– threatening to make new pictures, always backing away from them due to lack of funding. Turns out he’s been making a movie behind our backs: last week he announced that he’d be showing his next film, Upstream Color, at Sundance this January. Exciting! Of course, we’re talking about the man behind Primer, which is to say that the film we get will be complex, layered, and demanding. The trailer, which premiered today, seems to support this suspicion: Honestly? I have no idea what to make of this. I think it looks…