I thought because Elder Titan shares the same voice actor as Bill from L4D, along with Father Gregori from HL2 (both obviously related with their zombie killing). That maybe he should have lines when killing/killed by Undying. I mean, Undying already has the Lamarr reference, and about 10 other L4D references that it'd be pretty cool to hear Elder Titan saying something along the lines of "Across all planes of existence,Undying,our spirits must clash" or Undying: "Again we meet...and again we consume". Anyways, thought it'd be an interesting reference to the two.