Any Idea why my Explosion sound is NOT playing ?

I am working on a game shooting alien spacecraft, my script for destroying them is working fine but the sound is not playing upon the collision. The wav file has been converted to 2D and is attached to the script and an audio source which is attached to the object I want to destroy. Here is my script:

using UnityEngine;

using System.Collections;

[RequireComponent(typeof(AudioSource))]

public class collisionTest : MonoBehaviour {

public AudioClip Explosion2;

 void OnCollisionEnter (Collision other)
 {
 Destroy(this.gameObject);
 Destroy(other.gameObject);
 }
 void OnCollisionEnter(){
     audio.PlayOneShot(Explosion2,1.0F);
 }

}

I am not getting any warnings or errors upon pressing play. I am stumped.