grins like this. >> reporter: it may look like pleasant smiling to us. >> immigrants, they do not diminish america, they are america. >> reporter: but hill says it took away from amy klobuchar's gravitas. he compared to it walter mondale smiling too much when reagan joked about not exploiting -- >> my opponent's youth and inexperience. >> reporter: joe biden has plenty of experience, but our facial decoder cited hesitation. >> during the hesitation, the mouth would fall open a little bit. >> you did not raise your hand. did you raise your hand? >> no, no, i did. >> reporter: kamala harris got props for her unusual use of sadness. >> and that little girl was me. >> you really can't attack someone who's showing sadness, you're going to look like a heel. biden had no place to go emotionally. >> reporter: there's the face not physically. >> on the democratic debate stage but ever present. our facial expert says it's not so much the funny faces president trump makes but his