     using UnityEngine;
	 [RequireComponent(typeof(MeshFilter))]
     public class ReverseNormals : MonoBehaviour {
      
         void Start () {
             MeshFilter filter = GetComponent(typeof (MeshFilter)) as MeshFilter;
             if (filter != null)
             {
                 Mesh mesh = filter.mesh;
      
                 Vector3[] normals = mesh.normals;
                 for (int i=0;i<normals.Length;i++)
                     normals[i] = -normals[i];
                 mesh.normals = normals;
      
                 for (int m=0;m<mesh.subMeshCount;m++)
                 {
                     int[] triangles = mesh.GetTriangles(m);
                     for (int i=0;i<triangles.Length;i+=3)
                     {
                         int temp = triangles[i + 0];
                         triangles[i + 0] = triangles[i + 1];
                         triangles[i + 1] = temp;
                     }
                     mesh.SetTriangles(triangles, m);
                 }
             }        
             
             this.GetComponent<MeshCollider>().sharedMesh = filter.mesh;
         }
     }