不懂？还是不知道？

今天在Shichida上课，到了photo memory的环节。老师拿着两张相近的图画问iz

Sensei：“iz, which photo did you see just now?"

iz:"........" 咬着手指不停的摇头。

Sensei：“ok, please try again. Iz, which photo did you see just now?"

iz:"......." 一边奸笑，一边很串的摇头，结果每个大人都爆笑。老师拿他没办法，就让其他小朋友尝试。散课的时候，老师在评语簿里这样写着：“Dear iz，you are very clever, you know how to say no when you don't know the answer"

我很好奇的想问问iz：“你摇头的意思是不懂还是不知道？”