After hooking a Survivor, THWACK! activates:

The next time you break a Breakable Wall or a Pallet, all Survivors within 28/30/32 meters of your location will scream and reveal their Aura for 4 seconds.

Performing the Damage Generator Action on a Generator triggers Nowhere to Hide:

The Auras of all Survivors within 24 meters of your position are revealed to you for 3/4/5 seconds.

Increases the volume of Survivors Grunts of Pain by 25/50/50 percent.
Increases the volume of Survivors regular breathing by 0/0/25 percent.

Whenever a Survivor performs a Healing action while they are inside your Terror Radius, that Survivor suffers from the Blindness and Exhausted Status Effects
These effects linger for 6/8/10 seconds after the Healing action is interrupted by any means.