Flamethrower On Cortana (Mission 8)
There is a room near the beginning of the mission and off to the left of that romm is a crashed pelican. Around the pelican are some grenades and weapons. One of these weapons is the flamethrower, pick it up(it will switch to 3rd person view, and when you drop the flamethrower you still have the two weapons you had before you picked it up) because it is the best weapon in the game for killing flood.
Hope this helps!
Added by: gamesmaster285 Apr 22nd 2008, ID#2433