5301991f_and_The_Art_of_Breaking_Things__detailed_explanation
[signal] Forced laughter [part of body] mouth [possible meaning(s)] nervousness, cooperation [detailed explanation] 
Unnatural laughter is often a signal of nervousness or stress, as an effort to dispel tension or change the atmosphere. Artificial laughter is a signal of cooperation and a wish to maintain empathy.
“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