// Attach this script to a camera and it will 
    // draw a debug line pointing outward from the normal 
    function Update () { 
       // Only if we hit something, do we continue 
       var hit : RaycastHit; 
       if (!Physics.Raycast (Camera.main.ScreenPointToRay(Input.mousePosition), hit)) 
          return; 
       // Just in case, also make sure the collider also has a renderer 
       // material and texture 
       var meshCollider = hit.collider as MeshCollider; 
       if (meshCollider == null || meshCollider.sharedMesh == null) 
          return; 
       var mesh : Mesh = meshCollider.sharedMesh; 
       var normals = mesh.normals; 
       var triangles = mesh.triangles; 
       // Extract local space normals of the triangle we hit 
       var n0 = normals[triangles[hit.triangleIndex * 3 + 0]]; 
       var n1 = normals[triangles[hit.triangleIndex * 3 + 1]];    
       var n2 = normals[triangles[hit.triangleIndex * 3 + 2]];    
        
       // interpolate using the barycentric coordinate of the hitpoint 
       var baryCenter = hit.barycentricCoordinate; 
       // Use barycentric coordinate to interpolate normal 
       var interpolatedNormal = n0 * baryCenter.x + n1 * baryCenter.y + n2 * baryCenter.z; 
       // normalize the interpolated normal 
       interpolatedNormal =  interpolatedNormal.normalized; 
        
       // Transform local space normals to world space 
       var hitTransform : Transform = hit.collider.transform; 
       interpolatedNormal = hitTransform.TransformDirection(interpolatedNormal); 
       // Display with Debug.DrawLine 
       Debug.DrawRay(hit.point, interpolatedNormal); 
    }

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Update() {
        RaycastHit hit;
        if (!Physics.Raycast(Camera.main.ScreenPointToRay(Input.mousePosition), out hit))
            return;
        
        MeshCollider meshCollider = hit.collider as MeshCollider;
        if (meshCollider == null || meshCollider.sharedMesh == null)
            return;
        
        Mesh mesh = meshCollider.sharedMesh;
        Vector3[] normals = mesh.normals;
        int[] triangles = mesh.triangles;
        Vector3 n0 = normals[triangles[hit.triangleIndex * 3 + 0]];
        Vector3 n1 = normals[triangles[hit.triangleIndex * 3 + 1]];
        Vector3 n2 = normals[triangles[hit.triangleIndex * 3 + 2]];
        Vector3 baryCenter = hit.barycentricCoordinate;
        Vector3 interpolatedNormal = n0 * baryCenter.x + n1 * baryCenter.y + n2 * baryCenter.z;
        interpolatedNormal = interpolatedNormal.normalized;
        Transform hitTransform = hit.collider.transform;
        interpolatedNormal = hitTransform.TransformDirection(interpolatedNormal);
        Debug.DrawRay(hit.point, interpolatedNormal);
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Update():
        hit as RaycastHit
        if not Physics.Raycast(Camera.main.ScreenPointToRay(Input.mousePosition), hit):
            return
        meshCollider as MeshCollider = hit.collider
        if (meshCollider == null) or (meshCollider.sharedMesh == null):
            return
        mesh as Mesh = meshCollider.sharedMesh
        normals as (Vector3) = mesh.normals
        triangles as (int) = mesh.triangles
        n0 as Vector3 = normals[triangles[((hit.triangleIndex * 3) + 0)]]
        n1 as Vector3 = normals[triangles[((hit.triangleIndex * 3) + 1)]]
        n2 as Vector3 = normals[triangles[((hit.triangleIndex * 3) + 2)]]
        baryCenter as Vector3 = hit.barycentricCoordinate
        interpolatedNormal as Vector3 = (((n0 * baryCenter.x) + (n1 * baryCenter.y)) + (n2 * baryCenter.z))
        interpolatedNormal = interpolatedNormal.normalized
        hitTransform as Transform = hit.collider.transform
        interpolatedNormal = hitTransform.TransformDirection(interpolatedNormal)
        Debug.DrawRay(hit.point, interpolatedNormal)