5301991f_and_The_Art_of_Breaking_Things__detailed_explanation
[signal] Dropped-jaw smile [part of body] mouth [possible meaning(s)] faked smile [detailed explanation] 
More of a practiced fake smile than an instinctive one. The jaw is dropped lower than in a natural smile, the act of which creates a smile.
“I pretty much try to stay in a constant state of confusion just because of the expression it leaves on my face.” – Johnny Depp | Zen and The Art of Breaking Things
detailed explanation