From Kafka's "Letters to Felice"

Here he's writing to Grete Bloch again (she's been experiencing some dental pain):

However, there is no doubt in my mind that a draft doesn't cause toothache in healthy teeth. Healthy teeth don't even begin to feel well until they are exposed to a draft. And if the deterioration of the teeth wasn't actually due to inadequate care, then it was due, as with me, to eating meat. One sits at table laughing and talking (for me at least there is the justification that I neither laugh nor talk), and meanwhile tiny shreds of meat between the teeth produce germs of decay and fermentation no less than a dead rat squashed between two stones.