In Portland, Oregon yesterday, a little bird landed on Bernie Sanders' stage and then, while Senator Sanders was talking about it, the bird flew up on his lectern. His supporters went wild and, along with the Democratic candidate, took it as a sign. The little aviator has been dubbed "Birdie Sanders".

Note Senator Sanders' eyes. His eyelids are opened extremely. This lasted approximately 1.2 seconds.
This is eyelid configuration and its brevity are highly characteristic of sincere surprise.
Sanders' surprise was quickly supplanted by a sincere smile.
When a smile is sincere (Duchenne Smile) the eyes are always partially closed. Here his eyelids are nearly completely closed.
Although it's difficult to visualize, the lower eyelids also have the additional feature of an evanescent, concave-up furrow. This is another requirement of a sincere smile. What are the other features of a true smile?
In just a few seconds we see two classic and sincere facial expressions - first surprise, and then joy-happiness. When surprise is sincere, it always is very brief (usually just a second or two) and it's always followed immediately by a second sincere emotion (joy-happiness as in this example, anger, fear, disgust, sadness, etc.).
See also:
Nonverbal Communication Analysis No. 3508: Batman V Superman - Sad Affleck? (NOT!)
Nonverbal Communication Analysis No. 3504: Raúl Castro Lifts Barack Obama's Arm at Press Conference
Nonverbal Communication Analysis No. 3488: Donald Trump Brags about the size of penis - but His Body Language Indicates Anxiety/Deception
Nonverbal Communication Analysis No. 3491: Nancy Reagan, Ronald Reagan and Sincere Affection
Nonverbal Communication Analysis No. 2857: Barack Obama on Syria, Belief that Syrian opposition could have overthrown Assad with U.S. arms a "fantasy"
Nonverbal Communication Analysis No. 3331: Mila finds out Adam Levine got married - Rapid Transitioning of Emotions
Nonverbal Communication Analysis No. 55: Sincere Smile or is it Insincere?
Nonverbal Communication Analysis No. 3190: Taylor Swift's Body Language of Feigned Surprise
_____________________________________________________________________________________