אֱדַ֤יִן מַלְכָּא֙ זִיוֺ֣הִי שְׁנ֔וֹהִי וְרַעיֹנֹ֖הִי יְבַהֲלוּנֵּ֑הּ וְקִטְרֵ֤י חַרְצֵהּ֙ מִשְׁתָּרַ֔יִן וְאַ֨רְכֻבָּתֵ֔הּ דָּ֥א לְדָ֖א נָֽקְשָֽׁן׃
Then the king’s countenance was changed in him, and his thoughts affrighted him; and the joints of his loins were loosed, and his knees smote one against another.
Rashi on Daniel
and the belts of his loins became untied The belts of his loins opened because his loins were emptying out of fear, and his belt opened.