אַחֲרֵ֨י מִ֤י יָצָא֙ מֶ֣לֶךְ יִשְׂרָאֵ֔ל אַחֲרֵ֥י מִ֖י אַתָּ֣ה רֹדֵ֑ף אַֽחֲרֵי֙ כֶּ֣לֶב מֵ֔ת אַחֲרֵ֖י פַּרְעֹ֥שׁ אֶחָֽד׃
After whom is the king of Israel come out? after whom dost thou pursue? after a dead dog, after a flea.
Ibn Ezra
Scripture says an abomination in this case, because the act is forbidden, and in the case of the price of a dog, because it is disrespectful.