It depends on the individual. The only way I can describe it is the actors have a coating of blood on them and they'll react to you being visually seen moving and or creating loud noises etc.Heard rumours that you may have got splattered with Fake blood/Slime. Was that true?
If you think of a bat and how they use sound to find stuff. The game plays out sort of like that, you'll only get touched with blood (marking you down losing you points) if your careless about your stealth around the maze. Its kind of tactical in a way, the way the actors interact with guests seems to be only in certain scenario for the majority of the game. Then you do a run through of the maze as normal.
Some new makeup shots:
ToTT Vamp:
Awesome guy found in Dark Apocalypse / Lockdown.
More troubled infected:
The Nox Infernus ladies:
Molly Crowe isn't all bad, a selfie!