word. a facial decoder told cnn's jeanne moos what to look for. >> reporter: sometimes the faces debate candidates make are debatable. who better to dissect then than the guy who wrote the book? actually, several books on facial decoding. dan hill has advice for the dems based on previous performance. >> glare and stare and full of grima grimaces. you have to come across as someone's going to occupy the white house, not burn the place down. >> reporter: he points the finger at bernie sanders. oh, yes. you, bernie. >> nothing will change! >> reporter: president george w. bush once looked so cranky during a debate that the democrats turned it into a negative ad. called it "faces of frustration." okay, not too annoyed but not too smiley either. >> the biggest thing you shouldn't do is big, cheesy