Enemy Chatter

Sometimes, to show that the enemies aren't just mindless NPCs whose sole purpose is to provide a threat to the player, the developers may throw in some dialogue here and there if the enemies can speak the same language as the hero. This can either be the dialog equivalent of a random encounter, in which they mindlessly babble from a handful of pre-selected phrases (i.e. "Did you see anything?"), or entire scripted sequences with full-blown dialog between two or more enemies. Also, this serves as an Anti-Frustration Feature, particulary in stealth and survival horror games and levels, as it allows a more immersive means of allowing the player to figure out what the enemy is doing without mechanics like a heads-up display or radar. Having enemies loudly announce "I heard something!" or "go check it out" allows the player to know they've been detected, hearing something like "must be my imagination" or "I'm just seeing things" clues the player in that the enemies failed to find them and are returning to their regular behavior, and hearing "I see him!" or "throw a grenade!" alerts the player to run for cover. It's a double-edged sword — when done well, it can make the enemies seem human and allow the player to run rings around them, when done poorly, it can make the enemies seem even more like just robots. They're still mindless NPCs whose sole purpose is to provide a threat to the player, but now they have personality, and the player may feel sorry about killing them (well, depending on circumstances, the dialogue might just as well establish the NPCs as being major Jerkasses anyway). Retirony may also be used to further hammer the point home. If the chatter shows how terrified the NPCs are of you, you're participating in a Mook Horror Show.