Jewish and Irish Law
One of the striking features of ancient Irish law is that it was privately enforced. If the judge rules that Shawn owes Ian the value of 15 cows as compensation for an injury but Shawn declines to pay, Ian's response is not to ask some authority to enforce the verdict—there is no authority responsible for enforcing court verdicts. It isn't even, as in the corresponding Icelandic situation, to go back to the court and have Shawn outlawed.
The Irish solution is distraint. The first step is for Ian to formally give notice to Shawn that he intends to seize fifteen of his cows. Shawn then has a period of from one to five days—the exact length depends on the details of the case—in which to pay up. If he doesn't, Ian is entitled to enter Shawn's land early the next morning, accompanied by a professional law agent, seize fifteen cattle, and drive them to a private pound, a field on his own property or, with permission, on someone else's.
There is then another period of days during which Shawn can pay up and get his cattle back. Once that has expired, the final stage of the process begins. Each day, cattle to a specified value forfeit to Ian, until eventually all fifteen have forfeited and the debt has thus been paid.
As I mentioned in an earlier post, one interesting feature of Jewish law is the way in which it deals with ambiguous cases. If it is unclear whether Joseph does or does not owe a certain amount to Simeon, the usual rule is that the court will not compel Joseph to pay but, if Simeon has seized property of Joseph's corresponding to the amount Joseph might owe him, the court won't compel Simeon to give it back. The underlying principle is that the court can only make you pay money if there is reasonable proof that you owe it. There is no proof Joseph owes the money, so the court won't make him pay it. There is no proof Joseph doesn't owe the money, so if Simeon has seized it the court won't make him give it back.
Comparing the two systems, the obvious suspicion is that Jewish law is built on the remnants of something like Irish law, a system where plaintiffs executed their own judgments by seizing property. In the version of the law that we encounter in Maimonides, the Talmud, and the Mishnah it is assumed that by the time the court gets involved in the case, the plaintiff may already have taken action on his own behalf. Doing so creates a new status quo, and the court requires adequate proof—that the money was not owed—to change it.