It's difficult to pull off, but if you do well at being stealthy in Far Cry 2, enemies will begin royally freaking out to the point of vastly over-estimating the number of guys they are dealing with. It is extremely satisfying to hear a panicked mook scream "I-I dunno, there must be six or seven out there!"
You don't even need to be extremly stealthy to provoke such reactions. Kill two guards without being seen nd you'll hear "Okay, we must find the guy that killed our men. -How many are they ? -I don't know." Or a guard saying that he won't go search you because he doesn't want to die.