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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

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.