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I was thinking of different people crying, or better said just the moment before they start crying. Did you also see the shaking, most likely they are very nervous, the hands are shaking, sometimes it is the whole body? Is it a crying part or is it the attempt to not cry?
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It might depend on the emotion involved. Grief/trauma or fear/stress I think tends to cause shaking of the body.
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Personally, I've noticed that someone attempting NOT to cry will usually clench their muscles tightly and not shake. They may even hold their breath to attempt to keep control. If you break the control, you will more likely than not induce crying.