Channing Tatum is one of the best of his generation at understanding his physical self and using it in interesting ways, from the dancing in Step Up and Magic Mike, to the unexpected action scenes in Haywire, to the stillness of the athlete he played in Foxcatcher, to his talent in comedy. He has not only a dancer's understanding of dance itself, but a dancer's understanding of his body and how it plays in different settings. Here, he takes a character who is introduced as a perfect specimen and finds the guy's inner doofus. And it's not just through pratfalls—it's through small, smart choices (how he runs, how he crouches, how he stands, what he looks like when he's scared) that strip away cover-model swagger and emphasize that an action hero is not just a guy who goes to the gym.
This kind of being funny is also one of Sandra Bullock's strengths. She's always been good in comedies and in action movies with comedy elements, like Speed, in part because she understands not only how to deliver jokes, but how to look funny. Most of Miss Congeniality is about this; she is why it works. And there's a moment in While You Were Sleeping in which the great Jason Bernard, playing Bullock's boss, gives her a blunt assessment of her standing as the fake fiancée of a man in a coma, and she makes what might be the most inspired "yikes" face of the '90s. When people think of physical comedy, maybe it's more traditional to mean broad and big sequences, but these are both actors whose talent in comedy is closely connected with how well they understand what looks funny.
They're also both very good at turning on a dime; there's a scene in which they do get to dance together (if you're going to be in a romantic comedy with Channing Tatum, you should certainly get to dance with him), and as silly as the rest of the movie is, that scene is pretty sexy. And refreshingly, even though there's more than 15 years between Bullock and Tatum, nobody talks about it—just like they rarely talk about it when men in romantic films are significantly older than the women they play opposite.