add DoTween and use it for animating mouth scaling

Assets/_PROJECT/Scripts/NPCController.cs

@@ -1,20 +1,21 @@
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
+using DG.Tweening;
 
 public class NPCController : MonoBehaviour
 {
-    private Transform mouthTransform;
     private Vector3 mouthClosedScale;
     private Vector3 mouthOpenScale;
     private bool isTalking;
 
+    public Transform mouthTransform;
     public float mouthScalingMultiplier = 2.5f;
+    public float mouthMovementDuration = 0.25f;
 
     // Start is called before the first frame update
-    void Start()
+    void Awake()
     {
-        mouthTransform = transform.GetChild(0).transform;
         mouthClosedScale = mouthTransform.localScale;
         mouthOpenScale = new Vector3(mouthClosedScale.x, mouthClosedScale.y * mouthScalingMultiplier, mouthClosedScale.z);
 
@@ -48,13 +49,13 @@ public class NPCController : MonoBehaviour
 
         if (mouthTransform.localScale == mouthClosedScale)
         {
-            mouthTransform.localScale = mouthOpenScale;
+            mouthTransform.DOScale(mouthOpenScale, mouthMovementDuration);
         }
         else
         {
-            mouthTransform.localScale = mouthClosedScale;
+            mouthTransform.DOScale(mouthClosedScale, mouthMovementDuration);
         }
 
-        Invoke("MoveMouth", 0.5f);
+        Invoke("MoveMouth", mouthMovementDuration + 0.01f);
     }
 }