當身體碰到自己的身體
在body的inspector點選add component，再選circle collider，接著在上面的tag也給他obstacle
接著把物件大小調整到自己覺得合適的的大小就好了

讓角色在每一次開始的時候都在中心點
完整程式碼：

using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Rendering;

public class Snack : MonoBehaviour
{
    Vector3 direction;
    public float speed;
    public Transform bodyPrefab;

    public List<Transform> bodies = new List<Transform>();
    void Start()
    {

        Time.timeScale = speed;
        ResetStage();
    }

    void Update()
    {
        if (Input.GetKeyDown(KeyCode.W))
        {
            Debug.Log("W");
            direction = Vector3.up;
        }
        if (Input.GetKeyDown(KeyCode.A))
        {
            Debug.Log("A");
            direction = Vector3.left;
        }
        if (Input.GetKeyDown(KeyCode.S))
        {
            Debug.Log("S");
            direction = Vector3.down;
        }

        if (Input.GetKeyDown(KeyCode.D))
        {
            Debug.Log("D");
            direction = Vector3.right;
        }


    }
    private void FixedUpdate()
    {
        for(int i = bodies.Count - 1; i > 0; i--)
        {
            bodies[i].position = bodies[i - 1].position;
        }
        transform.Translate(direction);

    }
    private void OnTriggerEnter2D(Collider2D collision)
    {

        if (collision.CompareTag("Food"))
        {

            bodies.Add(Instantiate(bodyPrefab
            , transform.position
            , Quaternion.identity));

        }

        if (collision.CompareTag("Obstacle"))
        {
            Debug.Log("game over!");
            ResetStage();
        }
    }
    void ResetStage()
    {
        transform.position = Vector3.zero;
        direction = Vector3.zero;

        for (int i = 1; i < bodies.Count; i++)
        {
            Destroy(bodies[i].gameObject);

        }
        bodies.Clear();
        bodies.Add(transform);
    }
}