Hiding skill scream

[Variant]

So, I was wondering how TF_HIDING works. That is, how it can be used without triggering the skill scream (Hiding !!) on usage.

I thought it was in skill_castend_nodamage_id

case TF_HIDING:
case ST_CHASEWALK:
 if (tsce)
 {
  clif_skill_nodamage(src,bl,skillid,-1,status_change_end(bl, type, INVALID_TIMER)); //Hide skill-scream animation.
  map_freeblock_unlock();
  return 0;
 } else if( tsc && tsc->option&OPTION_MADOGEAR ) {
  //Mado Gear cannot hide
  if( sd ) clif_skill_fail(sd,skillid,USESKILL_FAIL_LEVEL,0);
  map_freeblock_unlock();
  return 0;
 }
 clif_skill_nodamage(src,bl,skillid,-1,sc_start(bl,type,100,skilllv,skill_get_time(skillid,skilllv))); 
 break;

But all those clif_skill_nodamage calls look the exact same as any other. Then I decided to look at LK_TENSIONRELAX (also in skill_castend_nodamage_id).

case LK_TENSIONRELAX:
 clif_skill_nodamage(src,bl,skillid,skilllv,
  sc_start4(bl,type,100,skilllv,0,0,skill_get_time2(skillid,skilllv),
   skill_get_time(skillid,skilllv)));
 break;

...That didn't shed much light either.

So my question is this:

How exactly does hiding the skill use scream work? Is it based on the ID (and therefore, on the client)? If so, is it something as simple as changing LUA files? Or, is it actually somewhere in the source and I just missed it?

I'm on rAthena rev. 15522.

Thanks!