Source: Bestiary 3, pg(s). 258
Sthenos possess the innate ability to communicate with snakes, including those that grow from their heads. A stheno's cranial snakes are semi-autonomous and move and act independently of their host and of each other, although their emotional state is influenced by the stheno's. They typically attempt to cooperate with the stheno's own actions, such as by attempting to aid her when searching for something or by joining in a physical attack against an opponent.
Sthenos can reproduce with humans. Stheno–human pairings will always produce either fully human or fully stheno children. There does not seem to by any clear pattern to determine what each child shall be; the determination appears to be mostly random.
Sthenos are a young species, having come into being a little more than a century before the present day. They originated when a powerful euryale named Stheno rebelled against Lamashtu, resenting the constant nightmares plaguing her as a result of the deity's dark blessing, and prayed to Shelyn for escape from her fate. Lamashtu slew Stheno for her rebellion, but the euryale's faith in her new goddess and determination to oppose Lamashtu caused the one hundred snakes that grew on her head to each transform into a new being, forming the first generation of the stheno people. Sthenos have since slowly spread across Golarion, increasing their numbers by reproducing with humans.
Sthenos have little unified society of their own, due to their low numbers and short history, and mostly live scattered across the nations of other peoples. They often have a difficult time finding societies that will accept them, due to their strong resemblance to medusas. When they find a community where they can settle down, sthenos prefer to become sedentary and have large families with many children, a desire thought to be motivated by their knowledge that they are still a young and rare people.
Sthenos have adopted many different faiths as they spread out, but many remain worshippers of Shelyn. They are also attempting to create new forms of art and culture specific to them, in an attempt to solidify their people's cultural identity.
Sthenos tend to be greatly fond of snakes, and often keep snakes as pets and as companions for the ones attached to their heads.