Cas watched Dean mill about the table, snatching a bit here and a kiss there. He noticed the lightness in his manner. It made him smile a little. He had to. It made him feel safe in a way most things didn't. Perhaps it was from years of Dean's worsening temper. Maybe it was just because no one liked being snapped at, even when they kinda deserved it. You learned to tolerate it but never any more than that.
When Dean sat beside him, when he say the real smile in his eyes, he returned it automatically. "You wanna tell me more about her?" Cas didn't feel for cars the way Dean did. He learned to drive because it was useful. Learned to repair them because it was necessary. It didn't mean he didn't know and notice what was important to Dean. He was trying to do the same thing with Jo too. He wanted to offer them things that were important to them, wanted to understand them. After years of feighning interest he was finally a little interested. "And, most importantly, when are you taking is for a drive?"