Siren Singing is a musical/voice-related magical ability that allows the user to put a person (usually a man) into an irresistible, hypnotic trance in which he will follow the mermaid around or obey the mermaid's whim and desires without question.
In this trance, the person does whatever they are told. In myths, sirens would sing their hypnotic tunes to attract and lure sailors to their deaths under the seas. The mermaids in the pod made the Enchantment Song strictly forbidden. However, Rita mentioned that sometimes when sailors or humans accidentally saw a mermaid, they need to be drowned and killed to preserve the secret, but since the Mako pod forbade the Enchantment Song, they drown them by making a storm. In other mermaid pods, however, it is unknown whether they allow the Enchantment Song to drown sailors.
There is also another type of siren singing. In the Northern Pod, they have their own siren song. This song can enchant Southern mermaids, but not Northern mermaids, since they are immune, as Mimmi reveals. In "The Siren", Sirena watches a video of a mermaid singing to a kayaker and becomes enchanted by the song. She becomes obsessed with David and follows him around. This song enchants a boy and makes him forget who he is.
The only way to reverse the Enchantment Song is to blow into a particular seashell.
When a mermaid uses the Siren Song during the Full Moon effect, the songs are reversed only when the full moon sets.