Does an AoO provoke AoO, and can splash weapons be used for an AoO?

[cmastah]

If character A starts to move away or use a maneuver without the appropriate feat, and character B makes an AoO but the AoO is a maneuver without the appropriate feat (like trip), does character A get an AoO against character B for that?

Also can you use a splash weapon for your AoO? What about if the enemy is in melee distance? If he smacks the foe with an acid flask (if he has to, to get to use the item) as an improvised weapon, could he apply the damage that way?

Also, if a wizard is TRIPPED while casting, how does that affect the concentration check? As there is no damage, does the DC simply become 10 + 0 (trip) + level of spell?

[Claxon]

Easy thing first, only melee weapons threaten. Splash weapons aren't melee weapons. Weapons that don't threaten wont allow you to make an AoO.

An alchemist flask used an improvised weapon wont deal it's acid damage and you would need to declare you were using it as an improvised weapon and your GM would determine what kind of damage it did (probably as a light club would be the closest thing).

As for your first question (if I'm understanding it correctly):
A performs trip (without Improved Trip) and provokes an AoO.
B performs trip (without Improved Trip.

And your question is: Does B also provoke an AoO from A?

Assuming A is threatening B with a melee attack, then yes A would get an AoO.

Being tripped could be ruled to be "vigorous motion" or even violent motion.

Situation Concentration Check DC
Cast defensively 15 + double spell level
Injured while casting 10 + damage dealt + spell level
Continuous damage while casting 10 + 1/2 damage dealt + spell level
Affected by a non-damaging spell while casting DC of the spell + spell level
Grappled or pinned while casting 10 + grappler's CMB + spell level
Vigorous motion while casting 10 + spell level
Violent motion while casting 15 + spell level
Extremely violent motion while casting 20 + spell level
Wind with rain or sleet while casting 5 + spell level
Wind with hail and debris while casting 10 + spell level
Weather caused by spell see spell
Entangled while casting 15 + spell level

[cmastah]

Thanks, I'm surprised about the AoO provoking an AoO from the original fellow but it's good to know the ruling.

Thanks for the help!

[Claxon]

That's why you typically don't do things that you would provoke for doing. Like combat maneuvers without the right feat.