How to make it flicker when looking at enemy?

http://answers.unity3d.com/questions/314145/create-white-flash-like-an-edit-on-whole-view.html

You keep asking the same question :

http://answers.unity3d.com/questions/319733/how-to-make-enemy-kill-you-if-starring-at-it.html

http://answers.unity3d.com/questions/321172/play-sound-when-looking-at-enemy.html

Just so it cannot be said that I wasn't constructive or helpful :

http://answers.unity3d.com/questions/287355/slender-like-game.html

http://answers.unity3d.com/questions/296068/how-to-make-a-slender-man-follow-character-script.html

http://forum.unity3d.com/threads/134862-Slender-$$anonymous$$an-Design-Outline

http://forum.unity3d.com/threads/141488-Slender-Beta-0.9

http://forum.unity3d.com/threads/138399-Slender-$$anonymous$$an-WIP

It's up to you to find the useful information among that. Read.

Break it down to one simple thing. Work out how to find if one object can "see" another. Once you do that, you can make it do anything you like with that as a trigger. And you can do it both for the player and the 'man' .