How to toggle on off animation in desired position

I'm creating my first unity game for learning how it works. the game: a player needs to avoid monsters by jumping over them. if it collides with a monster, the player dies and a stone thumb animation appear in its place. My Player script has an Animator responsible for stand/walk animation like this

private Animator isWalkingAnimator; 
isWalkingAnimator = GetComponent<Animator>();  //this is in Awake

void AnimatePlayer(string animatorName) //is called from Update
    {   
        Vector2 scale = transform.localScale;
        scale.x = playerWalkingState;       
        if(playerWalkingState != 0)//walk
        {
            isWalkingAnimator.SetBool(animatorName, true);  
            prevWalkingState = playerWalkingState;
        }
        else//stand
        {
            isWalkingAnimator.SetBool(animatorName, false);
            scale.x = prevWalkingState;
        }
        transform.localScale = scale;       
    }

in private void OnCollisionEnter2D(Collision2D collision) If the user collides with an enemy if (collision.gameObject.CompareTag("Enemy")) I wish isWalkingAnimator to show the thum stone animation

I've tried this: isWalkingAnimator.SetBool("isDead", false); but nothing happens