YSK: A very common cause of bad breath and/or bad taste in the mouth are tonsil stones: bits of plaque and food particles stuck in the tonsils. You can see them with your bare eye or with a black light pen and dislodge them by prodding the tonsil.
from /r/YouShouldKnow
YSK: 口腔异味和/或口腔异味的一个非常常见的原因是扁桃体结石：卡在扁桃体中的斑块和食物颗粒。你可以用你的肉眼或用黑光笔看到它们，并通过刺探扁桃体来清除它们。