Mesh Collider & Rigid Body fail to detect trigger

I have a pocketknife inside my project which I imported through a .blend (Blender) file.

I want to have it as a collectable item by the user and thus, I want it to rotate and disappear once the MainChar has collided with it.
So, I’ve added to the pocketknife a rigidbody (without the use of gravity because I want it to be on the air). Then, I’ve added to it a Mesh Collider whith ‘Is Trigger’ checked. Then I’ve attached this script to the pocketknife:

function OnTriggerEnter(hit:Collider){
    Debug.Log("Something hit me!");

I don’t even get the Something hit me! message…

You don´t need a rigidbody for this. Why don´t you ad a box collider, check “is Trigger” an try it this way?
Box Colliders are better for performance.

I found the solution: My collider’s size was set to (0, 0, 0) !

Altering the collider’s size fixed the problem.