Unity3D Coroutine编译器错误

我是unity的初学者，我正在尝试用协同程序播放动画，但出现了以下错误：

1.error CS1502:与UnityEngine.MonoBehaviour.StartCoroutine(System.Collections.IEnumerator)' has some invalid arguments 2.error CS1503: Argument#1"匹配的最佳重载方法无法转换System.Collections.IEnumerable' expression to type System.Collections.IEnumerator"

---

代码：

     using UnityEngine;
using System.Collections;
public class Trap : MonoBehaviour {
    //public float delayTime;

    // Use this for initialization
    void Start () {
        StartCoroutine (Go ());
    }
    // Update is called once per frame
    void Update () {
    }
    IEnumerable Go(){
        while (true) {
            animation.Play();
            yield return new WaitForSeconds(3f);
        }
    }
}

IEnumerable Go(){
    while (true) {
        animation.Play();
        yield return new WaitForSeconds(3f);
    }
}

IEnumerator Go(){
    while (true) {
        animation.Play();
        yield return new WaitForSeconds(3f);
    }
}