Deuteronomy 12:23

12:23 However, by no means eat the blood, for the blood is life itself ¹  – you must not eat the life with the meat!

Deuteronomy 19:21

19:21 You must not show pity; the principle will be a life for a life, an eye for an eye, a tooth for a tooth, a hand for a hand, and a foot for a foot. ² 

[12:23]  ¹ sn The blood is life itself. This is a figure of speech (metonymy) in which the cause or means (the blood) stands for the result or effect (life). That is, life depends upon the existence and circulation of blood, a truth known empirically but not scientifically tested and proved until the 17th century a.d. (cf. Lev 17:11).

[19:21]  ² sn This kind of justice is commonly called lex talionis or “measure for measure” (cf. Exod 21:23-25; Lev 24:19-20). It is likely that it is the principle that is important and not always a strict application. That is, the punishment should fit the crime and it may do so by the payment of fines or other suitable and equitable compensation (cf. Exod 22:21; Num 35:31). See T. S. Frymer-Kensky, “Tit for Tat: The Principle of Equal Retribution in Near Eastern and Biblical Law,” BA 43 (1980): 230-34.