Diprosopus or craniofacial duplication .Although 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 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.