Dean wasn't the sort who stayed on constant alert, really. He was observant, but not in the same way, really. He noticed things with an eye for art and beauty, not for who might creep up stairs behind him. Having his back to the stairs, staring out the window - neither struck him as odd.
"Usually not too out of bounds, during the day at least." They were meant not to come up outside of class, but it wasn't the sort of thing the Prefects would hound them about, probably.
Dean shrugged one broad shoulder. "If something seemed likely. Mostly just escaping listening to everyone go on and on about who's getting what team spot." He was more than a little wary, just talking to Theo. Slytherins usually didn't have much to say to him that wasn't them being prats to him, after all. Even if he saved them from giant squids - though Greengrass had been civil enough. "You just up for the view?"