How You Know He's Lying:

Dean: He won't look you in the eye no matter what. He hates lying to you but is convinced he's doing it to keep you safe. When confronted he gets scared that you'll leave him like everyone else.

Sam: He scratches the back of his head. He always feels guilty when he lies to you and only does it when he feels he has too. When confronted he wraps you into a hug, kisses the top of your head, and promises not to do it again. The promise is always broken but you can't stay mad at him for long.

Castiel: It is difficult to tell when he is lying but one of the tell tale signs is he will avoid you and when you do see him, will rarely talk to you. When confronted, he'll apologize and tell you he was doing it to protect you. You've tried to explain to him lying is wrong, but he just cocks his head to the side and refuses to understand.
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