Original sentence: The phrase "swan song" is a reference to an ancient belief that the Mute Swan (Cygnus olor) is completely mute during its lifetime until the moment just before it dies, when it sings one song
Edited sentence: The phrase "Swan song" is a reference to an ancient belief that the Mute Swan (Cygnus olor) is completely mute during its lifetime until the moment just before it dies, when it sings one heartbreakingly beautiful song