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Not just yawning, but cold too is contagious, find British researchers. A shivering person can make you feel cold, they add.
The team from University of Sussex found that volunteers who watched videos of people putting their hands in cold water found their own body temperature drop significantly.
The findings show that humans are susceptible to "temperature contagion".
"Such unconscious physiological changes may help us empathise with one another and live in communities," said neuropsychiatrist Neil Harrison who led the research.
"Mimicking another person is believed to help us create an internal model of their physiological state which we can use to better understand their motivations and how they are feeling," he explained.
Humans are profoundly social creatures and much of humans' success result from our ability to work together in complex communities.
"This would be hard to do if we were not able to rapidly empathise with each other and predict one another's thoughts, feelings and motivations," Harrison noted.
For the research, 36 participants each watched eight videos of actors putting their hands in either visibly warm or cold water.
At the same time, the temperature of their own hands was measured.
Their hands were significantly colder when watching the 'cold' videos. However, the 'warm' videos did not cause a change.
"We think that this is probably because the warm videos were less potent - the only cues that the water was warm was steam at the beginning of the videos and the pink colour of the actor's hand (whereas blocks of ice were clearly visible throughout the duration of the cold video)," the authors explained.
There is also some evidence to suggest that people may be more sensitive to others appearing cold than hot, they concluded.
The research was published in the journal PLOS ONE.