Another interpretation: "the awl" [with the definite article], to include the great awl. What is the implication? As Rava said regarding "the thigh," it means the most prominent part of the thigh; here too "the awl" means the most distinguished among awls. Rabbi Eliezer son of Yudan the eminent used to expound: one pierces only at the soft lobe. And the Sages say: a priest who is a Hebrew bondsman is not pierced, because he would thereby become blemished. And should you object, let him become blemished, Scripture says, "and he shall return to his family" (Leviticus 25:41), to the established standing within his family.
The Great Awl and Why a Priest Is Never Pierced
Yalkut Shimoni on Torah 317:4
דָּבָר אַחֵר, הַמַּרְצֵעַ, לְהָבִיא מַרְצֵעַ הַגָּדוֹל, מַאי מַשְׁמָע, כִּדְאֲמַר רָבָא, "הַיָּרֵךְ", הַמְּיֻמֶּנֶת שֶׁבְּיָרֵךְ. הָכָא נַמֵּי הַמַּרְצֵעַ, הַמְּיֻחָד שֶׁבַּמַּרְצֵעִין. אֲמַר רַבִּי אֱלִיעֶזֶר, (בַּר יוּדָן), [יוּדָן בְּרִיבִּי] הָיָה דּוֹרֵשׁ, אֵין רוֹצְעִין אֶלָּא בְּמִילָת, וַחֲכָמִים אוֹמְרִים, אֵין כֹּהֵן עֶבֶד עִבְרִי נִרְצָע, מִפְּנֵי שֶׁנַּעֲשֶׂה בַּעַל מוּם, וְיֵעָשֶׂה בַּעַל מוּם, אֲמַר קְרָא (ויקרא כה, מא) "וְשָׁב אֶל מִשְׁפַּחְתּוֹ", לַמֻּחְזָק שֶׁבְּמִשְׁפַּחְתוֹ.