Significance of the coughing? **Spoilers**
I noticed that, only after Elly's disappearance, both Shohreh and Sepideh are struck with coughing fits while trying to speak. They look and sound very real, not acted. Perhaps the actors all got colds, but why not re-take these scenes? Or maybe the coughing symbolises something?
Shohreh starts to cough while she and Ahmad are telling the children what to say to Elly's "brother". Ahmad picks up where she left off and she continues to cough - that seems improvised.
I thought Sepideh's cough might be caused by her going into the sea after Elly, but Shoreh did not go into the sea...