If Dean made those sandwiches, he wouldn't need Cas to eat them as a display of respect- Cas would do it of his own free will and he would make awesome sounds because they would be that good and Dean would get the ego boost his cooking skills frequently require of their own merit because he's an awesome goddamn cook and don't your forget it. As it stands, his agenda is a lot less self-serving than that for once.

"Damn positive. It was one of the trials to close the gate." Which Cas also doesn't know jack about, if memory serves correctly. At least, not all the details of it- he'd been keeping things pretty hush-hush ever since Cas brought down Samandriel in that fishy fucking rescue mission. All that's off the table now, though- Cas won't remembers it when he goes back home to a life of Biggerson's and Dean trusts him impeccably with this shit here in his right mind. "Pretty simple, actually. Just some sacred ground and a couple of vials of purified blood. Jab one in a demon's neck every hour on the hour and you've got yourself a handy Demon chicken soup for the soul."

He takes a pointed bite of his own sandwich, proceeds to talk with his mouth full. Rude. "Wasn't exactly perfect on Crowley- ground was kinda bullshit sacred, magic-produced with Wonderland's whateverness, and my blood ain't exactly pure even after I say fifty Hail Marys, but whatever. It did something. Toned his evil ass down from a ten to like a four so I'm counting it as a win."