NPC Abuse

NPC Abuse is a trick where a player pushes, interacts, damages or scares a friendly or hostile NPC in order to make him go to unintended locations and open locked doors.
Sometimes shooting the NPC will make it run to positions instead of walking. Be careful with guards though, as they will try to kill you and the only way to move them is to panic them with explosives so they go take cover.
In order for an NPC to be able to open locked doors, the map must be loaded using changelevel from the last map. If you load a save from that map, the trick will not work.

Notable uses

These are only short explanations of the trick uses in maps. For detailed explanations (and images), go to the map article instead.

• c1a2b - Interacting with Barney can make him follow you to the locked door. From there you can push him into the door and he'll open it for you.
  
  • You can also hit the zombie who's eating down at the tables, so he'll start following you. Get him close to the locked door and push him into it, so he can open it for you.
• c1a3 - Interacting with the scientist at a certain point to cut his sequence and make him follow you. Push him to the control room door so he opens it for you.
• c2a3c - If you use a grenade to scare a Vortigaunt to the door of the locked room leading to the freezer, the Vortigaunt will open it.
• c2a5f - If you manage to startle a soldier with a grenade and let him close the door which can only be opened by the security guard, he can open it. This NPC Abuse can also allow you to get infinite health, as this door is an Infinite Health Door.
• c3a2d - If you shoot the guard with gauss through the glass, you will startle him, prompting him to try hunting you down and opening the glass door. After that, you can use an explosive grenade to scare the guard into taking cover and opening the next door leading to the teleporter. That'll allow you to skip the Longjump module introduction cutscene.