The contact points generated by the physics engine.

Every contact contains a contact point, normal and the two colliders that collided (see ContactPoint). From inside OnCollisionStay or OnCollisionEnter you can always be sure that contacts has at least one element.

	function OnCollisionStay(collision : Collision) {
		for (var contact : ContactPoint in collision.contacts) {
			print(contact.thisCollider.name + " hit " + contact.otherCollider.name);
			// Visualize the contact point
			Debug.DrawRay(contact.point, contact.normal, Color.white);
		}
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void OnCollisionStay(Collision collision) {
        foreach (ContactPoint contact in collision.contacts) {
            print(contact.thisCollider.name + " hit " + contact.otherCollider.name);
            Debug.DrawRay(contact.point, contact.normal, Color.white);
        }
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def OnCollisionStay(collision as Collision) as void:
		for contact as ContactPoint in collision.contacts:
			print(((contact.thisCollider.name + ' hit ') + contact.otherCollider.name))
			Debug.DrawRay(contact.point, contact.normal, Color.white)

	// A grenade
	// - instantiates a explosion prefab when hitting a surface
	// - then destroys itself
	var explosionPrefab : Transform;
	function OnCollisionEnter(collision : Collision) {
		// Rotate the object so that the y-axis faces along the normal of the surface
		var contact = collision.contacts[0];
		var rot = Quaternion.FromToRotation(Vector3.up, contact.normal);
		var pos = contact.point;
		Instantiate(explosionPrefab, pos, rot);
		// Destroy the projectile
		Destroy (gameObject);
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    public Transform explosionPrefab;
    void OnCollisionEnter(Collision collision) {
        ContactPoint contact = collision.contacts[0];
        Quaternion rot = Quaternion.FromToRotation(Vector3.up, contact.normal);
        Vector3 pos = contact.point;
        Instantiate(explosionPrefab, pos, rot) as Transform;
        Destroy(gameObject);
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	public explosionPrefab as Transform

	def OnCollisionEnter(collision as Collision) as void:
		contact as ContactPoint = collision.contacts[0]
		rot as Quaternion = Quaternion.FromToRotation(Vector3.up, contact.normal)
		pos as Vector3 = contact.point
		(Instantiate(explosionPrefab, pos, rot) as Transform)
		Destroy(gameObject)