Joe Navarro, an ex-FBI agent and author on body language, notes:

• Harris wore her tension in her neck.
• trump would not look her in the eye.
• Harris’ chin showed her disbelief.
• trump’s uncomfortable tell: pursed lips.
• Harris openly laughed at him.
• trump pulled a ‘joker face.’
• Both used repeated blinks to display disagreement or incredulity.

— via POLITICO