The scientists haven't really done it for the cats, but hope the special mice will teach them valuable lessons about how to keep humans more healthy too.

Cholesterol has been linked to serious health problems in people, but until now it was thought we needed it.

Now by swapping cholesterol for something similar the experts hope they can learn important lessons.

The mice were smaller than normal, and couldn't have babies, but even the fact that they have grown to adults at all is a surprise.