Here Charlie Rangel is shown at a press briefing after the U.S. House of Representatives voted to censure him. His expression displayed here is the "Puffer Fish". It's seen almost exclusively seen just before or more commonly following a stressful event. I've seen great examples of this in surgeons after difficult surgeries, in athletes just prior to their games/events, in students just before big exams and in attorneys before trial. Always remember, a person's words will often be incongruent with their body language. It is much more reliable to trust the nonverbal message over the spoken word.
If you see the Puffer Fish - you can be sure that a major stressful event is immediately anticipated (of which the outcome and expectation is generally known) or just has taken place. If the display of stress seems out of place with the event, this should raise a big red flag in your mind.
The Puffer Fish nonverbal is associated with a decreased in respiration, heart rate and blood pressure and it occurs during exhalation (although it may occur over several cycles of respiration). The Puffer Fish's purpose is to have a calming effect.