Why is this script not working?

In this question I was given part of a script and told to attach it to my player. There are no errors, but the script doesn’t seem to do anything. Here it is:

var DeathSpeed : int; 

function Update(){

}

function OnCollisionEnter(collision : Collision)
{
if(collider.relativeVelocity.magnitude > DeathSpeed)// where "someValue" is a variable of your choosing.
{
Debug.Log("DEAD");// You'll have to implement how the player will die, yourself, but just call the function(s) needed to kill them, here.
}
}

Can anyone help?

Change if(collider…) to if(collision…)

http://docs.unity3d.com/Documentation/ScriptReference/MonoBehaviour.OnCollisionEnter.html

Does one of the objects have a rigidbody attached to it? As OnCollisionEnter requires it.