Diferent animations and triggers

Hi, I got a model with diferent animation names(like "Falling" animation, when the unit is falling), I tried to play the animation in game using "play animation" trigger but it didnt work, I used it to play normal unit animation(like attack) and it worked.
So I was wondering if it is posible to do it using jass or other trigger. plz I need help

there is a jass function which will allow you to play a unit's animation by index, give me a sec to find it.

EDIT: its called SetUnitAnimationByIndex, you have to call it through the custom script action like this:
Custom Script: call SetUnitAnimationByIndex( udg_someunit, 0)
which will play the first animation that the unit has.

also, warcraft can only understand certain animations, like stand or walk, you can try to change the animation name to "stand first" or something that u saw on another unit and see if it works.

might not be entirely ontopic, but how can you tell what animation index number you need for what animation?

like attack - 1 and attack -2, are different animations, still if you apply one in the GUI, it will just do one of the two.
how can you seperate that with using a custom script?

I often convert the model's mdx file to mdx and count the index of the animation myself

So I propose I need a wc3viewer in order to get the index number....(I need it's very frustrating when a unit does one of those 2 cause there different, and especially in cinematics you need precision

xcuse for being such a noob but what r the index numbers in the models

They are used to refer to the animation that is casted, so eacht animation on a unit has a index number in Jass script