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.

While carrying a Survivor you benefit from the following effects:

Decreases Wiggle effects, which cause you to strafe sideways, by 75 percent.
Increases Wiggle duration by 4/8/12 percent.

Any Survivor who blinds you or stuns you using a Pallet becomes the Obsession.
Anytime your Obsession switches to another Survivor by any means, that Survivor then suffers from the Oblivious Status Effect for 40/50/60 seconds and their Aura is revealed to you for 4 seconds.
You can only be obsessed with one Survivor at a time.

Unlocks potential in ones aura reading ability.  Each time a generator is fully repaired, Survivors within 16 meters of the completed generator will be revealed for 5 seconds.  When the last generator is fully repaired, all the survivors auras are revealed for 10 seconds.

You become obsessed with one Survivor.  Your Obsession gains a 33percent action speed bonus to unhooking and healing other Survivors.  Each time you hook a Survivor other than the Obsession, if the Obsession is alive, gain a token.  If the Obsession is alive, all Survivors who are not the Obsession get 3percent penalty to repair, healing and sabotage speeds for each token.

You reduce the duration of pallet stuns by 50percent.  Has no effect while carrying a Survivor.