[@Lady Amalthea] What you say it's true but what I'm thinking is that if character C sees A with a chicken head it's realistic to say that he shouldn't really know why character A wears that.
My angle (if you wanna call it like that) is that when I RP a character, I know what he knows, I see what he sees etc. 

Also. You've made me think about the issue a little. Thank you for a complete answer.

[@Ammokkx] That should be done via a GM post, I think