Kevin Moran can be seen proposing to his then girlfriend, soon to be fiancée, Molly McGinnis in the above viral video. By popping the question in a photo booth, he captured a beautiful nonverbal moment of surprise on Molly's face (0:32) - yet there are also some very telling expressions of his own.
The image below (0:28 seconds) shows Moran's central forehead contracted and elevated (along with his inner eyebrows) - indicative of the high level of emotion accompanying such a moment. In addition his jaw thrusts laterally (0:28 - 0:29) in a body language dynamic known as a "Jaw Confessional". There may also be lip and other facial components accompanying this facial tell.
A jaw confessional is a very brief duration & lateral movement of the jaw - indicating an anticipated embarrassment or risk of embarrassment and emotional vulnerability (There often is a verbal apology or similar statement immediately afterwards and if displayed in this setting it would be indicative of high sincerity. If you don't hear a verbal message of this type when a jaw confessional is seen, you can be sure that these emotions are being felt - just not expressed. In such a context, this verbal-nonverbal disparity should set off alarm bells). In the above scenario, Mr. Moran runs the risk of Molly saying "no" - thus he's risking significant embarrassment.
Be warned though - for when the jaw moves slowly to one side and lasts for a significantly greater duration - this body language indicates a completely different emotion.
Congratulations Kevin & Molly!
Nonverbal Communication Analysis No. 3041: Jim Harbaugh Body Language Tutorial
Nonverbal Communication Analysis No. 2929: Jessica Alba, Sin City 2, Action Figures and the Jaw Confessional
Nonverbal Communication Analysis No. 2776: James Franco's Mea Culpa - Body Language Tells
Nonverbal Communication Analysis No. 2314: Naomi Watts Pre-Oscar Interview and her Body Language of the "Jaw Confessional" and the Sincerity Quotient