The concept of two-headed people is a fictional trope. It's often used in mythology, folklore, and fantasy literature. Here are some possible reasons you might be thinking of this:
* Folklore and Mythology: Many cultures have stories about mythical creatures with two heads. These stories often symbolize duality, power, or even monstrosity.
* Fantasy Literature: Fantasy books and movies often feature characters with unusual physical traits, including two heads. These characters are usually designed to be unique and memorable.
* Medical Anomalies: While there is no record of someone living with two fully formed heads, there are rare medical conditions like Craniopagus, where twins are born conjoined at the head. This condition is extremely rare, and most cases are not viable.
If you have more details about this "Tancredi" story, like a specific source or location, it might help to find the information you're looking for.