There was originally going to be a song featured in the game called "GLaDOS' Song". It was written and performed by Ellen McLain, the voice actor for GLaDOS. She wrote the song for use as an Easter Egg in the game but it was ultimately never used.

The song was actually recorded after the game's release, and was performed by both Ellen and her husband, John Lowrie, the voice of the Sniper from Team Fortress 2. It was later modified by Harry Callaghan to sound closer to GLaDOS' synthesized voice.