The thing with Roadkill is that it's knowing that Sam and Dean also know the twist that makes it all make sense. And so when I first watched it, they seemed out of character, and I was thinking, oh no, is this episode badly written, is this a sign that the show is going downhill to sucktasticness and incoherency, yadda yadda. Yeah, sometimes my paranoia about TV does detract from my enjoyment.