Combat knife stuns and techniques confusion

I have some questions regarding the melee system and techniques. Since I’m playing localized version, some names may be not precise, sorry for that.

I have started playing a mall cop scenario. As the very first action I created myself a cudgel, since it had three techniques listed in its description. And it was a very good decision: cudgel does weak but very fast normal hits (due to rapid attack), and if it crits, then the enemy is reliably stunned (due to precision attack), making it easy to smash him to death safely. I have spent quite some time fighting with cudgels, and my melee skill has raised to something like 5 or 6.
Then I found a combat knife and decided to train piercing weapons skill with it. To my surprise, each combat knife critical hit also stuns the enemy, although it has no techniques listed.
Recently I have found a grappling hook and tried to use it in combat. It has rapid attack and spinning strike techniques listed in description. I have no idea what spinning strike is (have not seen it yet). As with combat knife, each critical strike stuns the enemy. Also I have noticed that rapid attack reduces attack time only by about 15% instead of standard 50% listed in wiki (according to last action duration display).

I do not know any martial arts yet. I play the latest stable build 0.C.

So the questions are:

  1. Why can I reliably stun everyone with combat knife and grappling hook on crits?
  2. Since each weapon stuns on crits, what’s the purpose of precision attack then? If there is any effect, how does it stack with ordinary stuns from crits? Is there any benefit from having precision attack on a weapon?
  3. Is it possible to learn techniques, so that it could be used in future with a weapon which does not provide it?
  4. Is it true that rapid attack may have different speed/damage modifiers on different weapons?
  5. What is spinning strike technique?
  1. Critical hits seem to do a lot of stunning in general, though for rather short duration.
  2. Precision strikes are not familiar to me.
  3. You cannot learn techniques from weapons, use a weapon that has the techniques you like. However, some martial arts allow you to use their techniques with specific weapons.
  4. I recall rapid strike being exactly twice as fast as normal attack, but I have not paid a lot of attention to move costs lately. Perhaps rapid strike was considered too effective and was nerfed.
  5. Spinning strike hits all enemies around you, it requires at least 3 monsters in adjacent tiles to use and is rather slow. It has been a while since I used it. If you do not want to manually move into each enemy (high spawn rate or a vault) consider a martial art that allows counter attacks.