Trip attack rule question

[Gordy95]

So, I'm running an optimized build: attack of opportunity abusing, crit fishing, power attack cheesing, infinite combo wielding monstrosity of a dwarf (don't judge for playing dwarf in an optimized build, it's a personal flavor thing).

Anyways, in doing the research for my critical wombo combo (TWF aptitude sizing Kukri, lightning mace feat, disciple of dispater 9-20 crit range) I've found an interesting addition: The knock-down feat.

Benefits
Whenever you deal 10 or more points of damage to your opponent in melee, you make a trip attack as a free action against the same target.

My question is, can a trip attack be critical, or at least threaten one? Because if it could be considered a threatened critical it would activate lightning mace for an additional free attack. This would be very very powerful, because if for some reason my wombo combo starts to slow down and I'm running out of attacks, I could proc additional attacks by using the knock down effect to get a free trip, likely crit on that, and use that free attack proc to make more free lightning mace attacks. In the end my turn should looks like this:

Turn starts
|
|
normal attack
(crits, activating lightning mace (LM). ten damage, activating knock down(KD))
| |
| |
Free LM attack Free KD attack
Activate LM & KD. |
| | |
| | (crits, procs LM, or is incapable of crit?)
Free LM attack Free KD

(Etc...)



Hope that wasn't too convoluted, just looking for ways to make my infinite chain a bit more infinte and branching. thoughts on whether or not the melee touch attack from trips can be critical, or any other ways to keep cheesing would be nice, thanks all.

[Galvin]

No. A trip attack does no damage, thus there would be no damage to multiply.

[mattie_p]

If you successfully trip, you get a free attack anyway, as improved trip is a pre-req to knock down (Deities and Demigods version).

[Warlawk]

No. A trip attack does no damage, thus there would be no damage to multiply.

According to the SRD


Critical Hits (http://www.d20srd.org/srd/combat/actionsInCombat.htm#criticalHits)

When you make an attack roll and get a natural 20 (the d20 shows 20), you hit regardless of your target’s Armor Class, and you have scored a threat. The hit might be a critical hit (or "crit"). To find out if it’s a critical hit, you immediately make a critical roll—another attack roll with all the same modifiers as the attack roll you just made. If the critical roll also results in a hit against the target’s AC, your original hit is a critical hit. (The critical roll just needs to hit to give you a crit. It doesn’t need to come up 20 again.) If the critical roll is a miss, then your hit is just a regular hit.

Increased Threat Range

Sometimes your threat range is greater than 20. That is, you can score a threat on a lower number. In such cases, a roll of lower than 20 is not an automatic hit. Any attack roll that doesn’t result in a hit is not a threat.


Nowhere does it say anything about damage being required. You can threat and crit with anything that requires an attack roll. If it deals no damage then obviously you do not deal double damage, but anything else that triggers off a threat or crit would still happen.