What exactly is collision.contacts[0]? What is inside of this array at index 0?
What exactly is collision.contacts[0];? So when something collides, the function OnCollisionEnter triggers, we get a collision object that has contactpoints? What is being stored in contacts[0]? x,y,z cords? also, this ContactPoint.point = Vector3 position.
collision.contacts[0]; is the first contact point of your objects collider with another collider.
ContactPoint class: http://unity3d.com/support/documentation/ScriptReference/ContactPoint.html
You can use collision.contacts*.point to create the collision effect (Sparks or something else)
* *More @ http://unity3d.com/support/documentation/ScriptReference/Collision-contacts.html
*