Bing-bong "This is your captain/flight attendant/whoever..."

[flyblue]

Interesting point Hamish. Stress is quite common in passengers, especially if something is happening that they don't understand. And believe me, this even covers a lot of normal stuff that happens in an aircraft but that is perceived as worrying and subsequently stressing by a large number (hydraulic pumps noise, change of levels in flight, etc). And when people are stressed there are more chances they'll do something not very clever and not adapted to the actual situation.

There are three main factors of stress, whic are 1)facing an unknown situation 2) Not knowing how it is evolving and how it's gonna last 3) Not being able to take action.

Information from the crew stops the mechanism of stress, simply by explaining 1) what the present situationis is, 2)how it is likely gonna last and what is being done to solve it 3) that you can help by doing nothing and let the crew do whatever they're doing and not divert their attention from their tasks.
What might seem "simple" announcements, actually are Crowd Control at work