Deanna Troi shivering.
Shivering was a physiological response caused by a decrease in a lifeform's temperature. (DS9: "The Homecoming") It could also be a reaction to fear, or shock from blood loss. (DS9: "The Ship")
In 2370, Deanna Troi began shivering while suffering from the early stages of Barclay's Protomorphosis Syndrome. She ordered the USS Enterprise-D computer to raise the temperature at least three times before Worf set it back to standard. (TNG: "Genesis")
In 2372, following the birth of a reptohumanoid, it began to shiver. Tom Paris was uncertain whether newborns were supposed to shiver, and asked Neelix if it was normal. Neelix replied that he hadn't been around many newborns; Paris agreed. After the Talaxian wrapped it in his jacket, the hatchling stopped shivering. (VOY: "Parturition")