Attacks of Oppertunity

[Enferac]

Hello!

The following question is about paizo's Pathfinder:
I was wondering if anyone knows the rules about if an attacks of oppertunity "hits". It says it "'interrupts'the normal flow", when you take the action, but it doesn't say anything about if it hits. Will a hit stop the action? I find it logical and funktional when it comes to actions like "grapple", (The defender strikes the attackers arms, etc, to get him away).
I've been reading about AoO and more in the "combat" section of the book, but not been able to find anything about this. If anyone knows anything at all about this, or if you have any "house rules" applications or thoughts about this, I'd appreciate a response. It might be as simple as, I've missed it.

I've been reading some d&d3.5 and it says if the AoO hits when an attacker perform a grapple check, the grapple attempt fails.
But it's not same game, and I prefer to read pathfinder as a new game with similarities to older d20 games.

I'm not english native, but I hope you are able to see my point.

Cheers!

[Are]

An attack of opportunity will not stop the interrupted action in most cases. However, if the attempted action is no longer possible as a result, then the AoO will effectively have stopped it (such as tripping someone who was attempting to move past you).

Some actions have special rules detailing what happens if an AoO taken as a response is successful. In the case of grapple attempts (and other combat maneuvers), the Pathfinder rules state that any damage taken as a result of the AoO is added as a penalty to the CMB roll.