- Original and Reversed (OpFor Easter Egg)

From the Combine Overwiki: “in the Opposing Force sound files can be found an apparently unused sound named that is actually heard during the Gene Worm scene. It is reversed and slower that normal. After some editing, it can be identified as a sentence spoken by Randy Pitchford, saying, 'To win the game you must kill me, Randy Pitchford.' This is a nod to a similar Doom 2 Easter egg made by John Romero.“