From Valve Developer Community
- Waiting to Rappel? (waitingtorappel)
- If yes, this NPC spawns suspended in air and awaits a
BeginRappelinput. It will then spawn a zipline and slide down. When it hits the ground, NPC will cut away the line and try to move forward a few feet to make room for the next NPC. The NPC will not attempt to clear its landing space if it cannot do so by taking a few steps forward.