Charles Darwin argued that animals can express emotions with their face and body , like humans do . Now researchers have found that rats can recognise pain the faces of their fellow rodents . The study suggests that as well as expressing their emotional state , the pained faces of rats may have a ‘ communicative function ’ . They may even use expressions to warn other rats of danger or ask for help . Researchers have found that rats can recognise pain the faces of their fellow rodents .Researchers based at different institutions in Tokyo , noted that rats flatten their ears , narrow their eyes and puff up their cheeks when they are in pain ( shown in the images on the right ) – an observation in previous studies . Researchers based at different institutions in Tokyo , noted that rats flatten their ears , narrow their eyes and puff up their cheeks when they are in pain – an observation in previous studies . The experts wanted to find out whether the rodents do this as a reflex reaction , or to communicate their discomfort to others . They found that Long-Evans rats can read pain on other animal ’ s faces and use the information to makes decisions , Popular Science reported . The scientists first took photographs of rats who were in pain and others with neutral expressions . To test the rodents ' response to rats ’ pained expressions , they showed them the photos in a specially made cage , to test whether they responded to the face , rather than the smell of another animal , for example . The rats chosen are described as ‘ naive ’ in the study , published in the journal Royal Society Open Science , and were between eight and 12 months old . Individuals were put into a cage composed of three interconnecting rooms , one of which had images of a rat in pain , which had been given an electric shock . To test the rodent ’ s response to rats ’ pained expressions , they showed them the photos in a specially made cage ( pictured ) . They found that rats spent less time in the room showing rodents in pain , than they did in the other compartment showing rats with neutral facial expressions . Male mice sing to woo females , scientists claim . They also change their tune depending on whether she is within sight or not . The females , meanwhile , seem to like some of the songs more than others . In a quirky study that could shed help shed light on autism and other conditions that involve difficulties in communication , researchers from Duke University in North Carolina studied male mice that were either placed in a cage with a female – or one with just her scent . Special equipment was used to record and analyse their squeaks , which are so high-pitched that people can ’ t hear them . This revealed that they sang one song when they could simply smell a female and another one when they could see her . When they could merely smell a potential mate , they belted out an extremely shrill and complex song , perhaps in an attempt to make themselves known . But when she was within sight , they serenaded her more softly . These songs also had a more simple structure and were longer . They entered one-by-one through a central compartment without any images on the walls and made their way to a compartment off the central room with pictures of pained rats on the walls and another offshoot room with photos of happier rats on the walls . Each rat was allowed to wander freely around the cage for 10 minutes while the researchers recorded how long it spent in each room . They found that rats spent more time in the rooms where they didn ’ t have to confront the image of a rat in pain . '…the rats stayed longer in the compartment with the images of neutral expressions than in that with the images of pain expressions , ’ the study says . ‘ This indicates that the rats were able to discriminate the category of emotional expression. ’ On average , they spent one minute less in the pain room , than the compartment showing a rat with a neutral expression . While the scientists didn ’ t say that the study suggests mice can empathise , they believe that their facial expressions have evolved to communicate pain . They wrote : ‘ emotional expression in rodents , rather than just a mere “ expression ” of emotional states , might have a communicative function. ’ ‘ The emotional expression of pain might have an adaptive function for both the expresser and receiver , such as emitting a warning signal or promoting carer behaviour from the receiver , ’ they hypothesised . Previous studies have shown that several kinds of primates make faces and can discriminate between different expressions .
Researchers in Tokyo placed rats in a cage with three compartments . One room showed photos of rats in pain , and another with neutral faces . Rats spent more time in the 'neutral ' room suggesting they recognise fear . Experts believe facial expressions are used to communicate with others .