In the episode of Lost entitled "The Moth" Sayid is shown setting off his Bottle Rocket to get the attention of Shannon on the beach. When the camera cuts to Shannon on the beach she is talking with a woman...this woman notices Sayid's rocket and points to it in the sky. This woman is the French woman Rousseau who has apparently been on the island for 26 years...but she is supposed to make her "first appearance" in the later episode where Sayid finds her.

Evidently, the producers used her previously as an extra.