Creatures with grab and a larger barbarian brutal pugilist AOO?

Question

I have a question about how the monster ability grab functions and a specific scenario.

If a creature with this special attack hits with the indicated attack (usually a claw or bite attack), it deals normal damage and attempts to start a grapple as a free action without provoking an attack of opportunity. Unless otherwise noted, grab can only be used against targets of a size equal to or smaller than the creature with this ability.

So if a medium creature with grab attacks another equal or smaller, it automatically tries to grapple. When a medium attacks something larger , does it still attempt that automatic grapple only to have it fail because of the larger size, or is no grapple even attempted?

This is important because of the Barbarian archetype Brutal Pugilist. At second level they get savage grapple.

She can make an attack of opportunity against creatures trying to grapple her even if they possess the Improved Grapple feat or the grab special attack.

If the barbarian is larger for some reason (either by race, enlarge person, 5th level ability from brutal pugilist, ...) will they get to make an attack of opportunity or not?

Answer 1

No.

grab can only be used against targets of a size equal to or smaller than the creature with this ability

It doesn’t say that the grapple fails, it says that the grab ability, wholesale, does nothing against a larger creature. Thus, no grapple attempt is ever made.

Moreover, it does seem like grab ought to be a voluntary thing in most cases, though the rules as written do not indicate it is.