What Once was Lost

 What Once was Lost is a soundtrack piece included in the Halo: Original Soundtrack. It runs for 1:42 minutes.

Appearances
It plays during the outside portion of the level 343 Guilty Spark, and also during a portion of Keyes. It adds to the tension the player feels before and after discovering the Flood. It primarily uses swamp noises such as animal cries, with undertones to add to the suspense. The soundtrack itself creates much of tension to suit the dark mood of the level.

Trivia

 * The title of the piece is probably named after the Flood. The title signifies the Flood's return to the Halo universe.
 * If you add the numbers in the run time it equals up to 7 (1+4+2=7).