Rav Zevid, in the name of Rava, said: the verse states (below, verse 25) "a wound for a wound" (Exodus 21:25), in order to require payment for pain in addition to payment for damage. But surely this clause is needed to teach that one who acts unintentionally is treated like one who acts intentionally, and one who acts under compulsion like one who acts willingly? If so, let Scripture write "a wound for a wound" [using the simple preposition]; what does the wording "a wound in place of a wound" add? Learn from this two teachings [both the equating of unintentional with intentional and the separate payment for pain]. How can you find a case of pain in a place where there is also damage [so that pain is paid for on its own]? Consider how much a person would be willing to pay to have his hand, already condemned to be cut off by royal decree, severed with a drug rather than by the sword. [The added suffering of one method over another is the measure of pain, paid for over and above the loss of the limb itself.]
Wound for Wound and Paying for Pain Alongside Damage
Yalkut Shimoni on Torah 333:1
רַב זְבִיד מִשְּׁמֵהּ דְּרָבָא אֲמַר, אֲמַר קְרָא (להלן פסוק כה) "פֶּצַע תַּחַת פָּצַע", לִתֵּן צַעַר בִּמְקוֹם נֵזֶק. הָא מִבַּעְיָא לֵיהּ לְרַבּוֹת שׁוֹגֵג כְּמֵזִיד וְאֹנֶס כְּרָצוֹן. אִם כֵּן לִכְתֹב "פֶּצַע בְּפֶצַע", מַאי "פֶּצַע תַּחַת פֶּצַע", שְׁמַע מִינָּהּ תַּרְתֵּי. צַעַר בִּמָקוֹם נֵזֶק הֵיכֵי מַשְׁכַּחַת לָהּ, כַּמָּה אָדָם רוֹצֶה לִתֵּן לִקְטֹעַ יָדוֹ הַמֻּכְתֶבֶת לַמַּלְכוּת בֵּין סַם לְסָיִף.