damn "simultaneous feedback"

i just took my intro to communications final & boy am i upset.
i missed a freaking question that i KNEW yet when i get to that question my mind goes blank.
i cant remember shit.
i sit there & stare at the paper for at least 10 minutes in hopes that if i stare at it enough it'll come back to me.
i end up being the last motherfucker in the class so i say fuck it.
soon as i leave, i pull out my notes & the answer was so effing obvious!
im mad as hell i missed it cuz i knew that shit inside out.

the question:
what are the two main differences between face to face and mediated communication?

answer that stumped me:
simultaneous feedback & lack of social roles

two meesly words. **blank stare**
damn that "simultaneous feedback"