I had to edit this, realising the condition is called Diprosopus; the cat should be not a Janus cat but a Diproso-puss
but not very........
This is what Wiki has to say:
Diprosopus (Greek διπρόσωπος, "two-faced", from δι-, di-, "two" and πρόσωπον, prósopon [neuter], "face", "person"; with Latin ending), also known as craniofacial duplication (cranio- from Greek κρανίον, "skull", the other parts Latin), is an extremely rare congenital disorder whereby part or all of the face is duplicated on the head.
 DevelopmentAlthough classically considered conjoined twinning (which it resembles), this anomaly is not normally due to the fusion or incomplete separation of two embryos. It is the result of a protein called sonic hedgehog homolog (SHH). (The unlikely-sounding name of this protein was inspired by the Sonic the Hedgehog videogame character and is part of an idiosyncratic naming tradition in molecular biology research that some have criticized as frivolous.)
The SHH protein and its corresponding gene have been found to play an important role in signaling craniofacial patterning during embryonic development. Among other things, the SHH protein governs the width of facial features. In excess it leads to widening of facial features and to duplication of facial structures. The greater the widening, the more of the structures are duplicated, often in a mirror image form. This has been demonstrated in the laboratory by introducing pellets of the SHH protein into chicken embryos, resulting in chickens with duplicate beaks. Insufficient amounts of that protein lead to opposite conditions such as cyclopia where facial features are insufficiently developed.
Healthy brain development is also dependent on the signaling function of the SHH protein. During embryonic development, the SHH protein directs embryonic cells to organize in specific areas that later become specialized neural tissues, thus controlling the size and shape of brain structures.
 OccurrencesDiprosopus often occurs in combination with other congenital disorders, particularly anencephaly, neural tube defect and cardiac malformations. When present, the brain may show abnormalities ranging from partial to complete duplication of brain structures, and/or underdevelopment of brain tissues.
Few two-faced animals have survived due to associated internal organ abnormalities and brain abnormalities. One of the most famous was Ditto the pig. Ditto was raised to adulthood, but died of pneumonia caused by food inhalation when breathing through one muzzle while eating with the other. In July 2006, a 6-year-old two-faced cat called "Frank and Louie" from Millbury, Ohio USA received publicity. In this latter case, only one esophagus (and possibly only one trachea) was functional and this aided survival.
Go Frankie& Louie!