Why Tom and Jerry can now be best friends

But now, a real-life mouse has been developed that is so fearless it will take on even the scariest of foes.

A 'switch' in the brain of mice which enables them to sense or smell danger has been discovered by scientists in Japan.

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By turning it off, they have created a mouse without fear, called Delta D.

When faced with the imminent smell of danger from a cat, Delta D simply scuttles over, gives a friendly sniff and snuggles up in the feline's soft fur.

The curious behaviour has so surprised cats that, instead of gobbling up Delta D, they have shown a measure of affection back.

Even though the innate fear of certain smells can be switched off, the mice can still learn a negative response from an odour if something bad happens to them - such as falling ill from rotting meat or a cat not being so friendly, the researchers found.

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Until now, many scientists have argued that all fear is learned.

But the findings suggest the presence of a system of innate responses, said Hitoshi Sakano, from the University of Tokyo, whose team bred the strain of mice.

He added that the mutant mice lacked innate responses to 'aversive odorants' - the smell of fear - even though they were capable of detecting-them. But they could still be conditioned for aversion.

Humans could have a similar system for discerning fear, the researchers said in their report in the journal Nature.

The findings follow the announcement last week that scientists in Ohio have created a 'super mouse' that can run 6km (3.7 miles) without stopping.

The mouse has a longer life expectancy, can also breed for much longer than normal mice and never puts on weight, despite eating 60 per cent more than average.