Jumping back into things, I just want to mention an interesting Ramban that I saw when learning Makkos with my son, which is sort of apropos of parshas hashavua (but then again, so is most of choshem mishpat). Eidim zomimim who testify that Ploni’s muad ox killed someone and Ploni must pay kofer do not get punished in turn by having to pay kofer; instead they receive malkos. The gemara (2b) explains that kufra kaparah, the payment is exculpatory for the person whose ox murdered; since the eidim zomimim do not have an ox which killed anyone, the payment is not applicable to them.
This is not the only place that we find that money paid as a kaparah takes on a different character than other payment. Tosfos (Kesubos 30b d”h zar) writes that mechila by the recipient does not exempt an obligation to pay kaparah.
The Ramban adds an interesting lomdus to the gemara’s explanation which sounds almost like something an acharon would say. The Ramban writes that kofer is a substitute for the ox's owner receiving misah b’ydei shamayim. It makes no sense to say that eidim zomimim through false testimony attempted to cause someone to be chayav a misah b’ydei shamayim – k’lapei shemaya, from Hashem’s perspective, the truth is always known, and no one can ever receive a misah b’ydei shamayim unjustly! (Compare with the Ramban’s explanation on chumash as to why if the nidon was killed, eidim zomimim are also exempt – Ramban explains that since Elokim nitzav b’adas K-el it is impossible for Beis Din to kill someone who does not deserve death.)
What makes the Ramban interesting is that he directs us to look at the mechayeiv, the root cause behind the payment, instead of just looking at the consequence (very R’ Shimon Shkop-ish). R’ Akiva Eiger points out based on the Ramban that the gemara’s chiddush is not just true of kofer, but would be true of any attempt of zomimim to be mechayeiv misah b’ydei shamayim.