If he blinded his slave's eye and [then] knocked out his tooth, he goes free [on account of the eye] and pays him the value of the tooth. Rabbi Zeira objected to this: say rather, [if] he blinded his eye, let the slave go out on account of his eye; [if] he blinded his eye and knocked out his tooth, let him go out on account of his eye and his tooth [taking nothing extra]. Abaye said to him: Scripture says "in place of his eye" and not in place of his tooth-and-his-eye; "in place of his tooth" and not in place of his eye-and-his-tooth [therefore the second injury is compensated separately]. What is the reason that the slave goes free through tooth and eye? Because it is written "and Ham, the father of Canaan, saw [his father's nakedness] and told" and so forth (Genesis 9:22).
Why the Canaanite Slave Goes Free by Tooth and Eye
Yalkut Shimoni on Torah 339:5
סִמֵּא אֶת עֵין עַבְדּוֹ וְהִפִּיל אֶת שִׁנּוֹ, יוֹצֵא לְחֵרוּת וּמְשַׁלֵּם לוֹ דְּמֵי שִׁנּוֹ. מַתְקִיף לָהּ רַבִּי זֵירָא, אֵימָא, סִמֵּא אֶת עֵינוֹ נֵיפוּק בְּעֵינוֹ, סִמֵּא אֶת עֵינוֹ וְהִפִּיל אֶת שִׁנּוֹ נֵיפוּק בְּעֵינוֹ וּבְשִׁנּוֹ. אֲמַר לֵיהּ אַבַּיֵּי, אֲמַר קְרָא, תַּחַת עֵינוֹ וְלֹא תַּחַת שִׁנּוֹ וְעֵינוֹ, תַּחַת שִׁנּוֹ וְלֹא תַּחַת עֵינוֹ וְשִׁנּוֹ. מַה טַּעַם הָעֶבֶד יוֹצֵא בְּשֵׁן וְעַיִן, מִשּׁוּם דִּכְתִיב (בראשית ט, כב) "וַיַּרְא חָם אֲבִי כְנַעַן וַיַּגֵּד" וְגוֹ'.