Tom and Jerry just wouldn't have been the same if it had featured one of Ko Kobayakawa's mice.

The Tokyo University professor has just unveiled mutant mice that have lost their innate fear of cats.

Rather than flee or freeze when confronted with their feline enemy, the mice sniffed and even played with them, blissfully unaware of the potential dangers.

Kobayakawa developed the fearless mice by shutting down receptors in their olfactory bulb - the area of the brain that processes information about smells - which would normally induce panic as soon as they get so much as a whiff of a cat.

In experiments with cats belonging to students, the genetically engineered rodents simply carried on as usual, sniffing and playing with their nemesis as if nature had intended them to be best friends.

"Mice fear cats because they are innately conditioned to fear when sensing the odour of the predators. So by getting rid of the specific receptors for sensing the odour, mice never feel afraid of cats," Kobayakawa told Reuters.

His research confirms the long-held belief among scientists that fear in animals is connected to their keen sense of smell.

"Once removing innate elements by which mice fear cats from them, we are able to make mice who can get along with cats," he said.

"So by applying this theory to other mammals, we will probably be able to make other animals that are not afraid of their natural enemies."

Inducing fearlessness in mice does not mean that cats, too, are ready to form unlikely friendships with their prey. Mochikko-chan, a cat used in a recent demonstration, was chosen because of her particularly docile nature.

Also, according to the researchers, even the modified mice froze in fear whenever the cats miaowed.