[Of course it has to be around Cas. She's kind of used to making small shields by now. Nothing this major, just enough to use as makeshift sunblock. She looks really proud of herself, but she's gotta concentrate to keep it up, so she's trying to keep doing that. Plus, from out here she can tell where the holes in the bubble are so she can repair 'em in a jiffy.]

Dunno. Kinda just comes to me. [A bit of a shrug.] It's to do with the stuff in the air.