Castiel has to bite his lips for a moment, because the mere prospect... the mere thought... It's enough to make him want Sam here, now, with him, enough to make him moan with want and desire.

He can't help it.

"The red ball gag, master. Please."

He can easily slip it out of his mouth if he needs to say something to Sam, but they both enjoy the way he sounds around it. Castiel runs his fingers over the collar in delight at the thought.