NPCs have the ability to keep themselves busy without the need for multiple, complex, scripted sequences. The Ai_goal_actbusy entity tells an NPC or group of NPCs to keep themselves busy by acting out certain sequences and animations with the help of info_node_hint entities. Basically, the info_node_hint entity depicts which animations to play, and the ai_goal_actbusy entity picks a random node for the NPC to walk to.

In order for the info_node_hint to tell an NPC what to do, you need to write a set of instructions that are located in a text file called actbusy.txt. This file is located in your scripts folder. For example, I'm using Half-Life 2: Episode Two, so my scripts folder is located at Steam\steamapps\half life 2. If you navigate to this folder right now, there might not be anything in it. Again, we'll need to use GCFScape to extract proper files. Extracting files will let us use Valve's actbusy.txt file, but we could always create our own. If you create your own actbusy.txt...