Cas stands up from the table they're studying at and Sam glances up to see him putting on his trench coat.
Dean asks what Sam was thinking, "Where are you going?"
"I really can't stay," Cas says.
"What? But… It's cold outside," Dean protests.
"I'm going away to visit my family tomorrow for winter break."
"But it's really friggin' cold outside!"
Sam places a hand over his mouth to keep from laughing.
"This evening has been very nice. Thank you for dinner, but I think you understand the concepts well enough now, you'll do fine on the test," Cas says, stepping away from the table.
"Yeah thanks," Dean says, "But what's your hurry?"
"My mother will worry if I do not arrive home on time."
Sam can't hold it in any longer and starts laughing so hard that he has trouble answering Dean when he asks him what's so funny, "You do- you do realize that the two of you basically just recited the lyrics to 'Baby It's Cold Outside' to each other, right?"
Dean and Cas glance awkwardly at each other before Dean blushes faintly and turns back to his notes, "Whatever. See you next week, Cas."
Cas nods a goodbye to Sam and lets himself out. Sam cracks up again as soon as he's gone. Sam really likes hanging out with Dean and Cas; he hasn't had so much to tease Dean about since his brother was going through puberty. Dean chucks his pen at him, and then belatedly realizes that he needs it.
Sam laughs harder, "Oh, this is going to be so much fun."