Doctors were baffled when they picked up an abnormality in the third trimester scan of a Charleston, South Carolina, mother. Their initial diagnosis included a cyst, a bone disorder or teratoma, which is when a twin absorbs another during development in the womb.
When the baby girl was born, they discovered that she had an extra lip, set of six teeth and even a small tongue that moved at the same time as that in her main mouth.
According to Sky News, the condition, called duplicated oral cavity, is so rare, that there have only been 35 recorded cases since 1900. The latest case has now been documented in BMJ Case Reports.
Also known as "second mouth", the condition is seemingly harmless. Immediately after her birth, a team of surgeons performed an operation to remove the additional feature.
Now six months later, the baby is almost completely unaffected, only suffering some swelling and a minor nerve defect in her bottom lip, Sky News also reported.
"Our patient's craniofacial duplication is a rare case that presented as an isolated anomaly, with no associated syndromes or abnormalities," the study authors noted.
"At six-month follow-up, the incisions were well healed and the patient was feeding without difficulty."
Also known as craniofacial duplication, duplicated oral cavity has been documented in animals, including chickens, cats, goats and pigs.
The last reported case involving humans include twins born in Sydney, Australia, in 2014 with one body and one head but two identical faces. Sadly, they died 19 days after birth.