וַיַּגְרֵ֤ס בֶּֽחָצָץ֙ שִׁנָּ֔י הִכְפִּישַׁ֖נִי בָּאֵֽפֶר׃
Il a broyé mes dents avec du gravier, il m’a roulé dans la cendre.
Shulchan Arukh, Orach Chayim
6. One who is able should only eat burnt bread in salt and a flask of water in the Parting Meal. Rema: There are those that are strict after eating the bread to dip into ash and to eat on the word(s) "And he has broken in gravel..." (Lamentations 3:15)