For the source text click/tap here: Nedarim 33
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We learned in a mishna: (Ketubot 13:2) Where a husband who went to a country overseas, and another man supported his wife on his own initiative and then demanded to be reimbursed for that support when the husband returned, Ḥanan said: The one who took the initiative to support the wife lost his money, since the husband neither asked him to do so nor committed to compensate him.
The sons of High Priests disagreed with him and said: The one who took the initiative to support his wife will take an oath as to how much he spent and take repayment from the husband.
Rabbi Yoḥanan ben Zakkai agreed saying any case of this type he placed his money on the antler of a deer, (i.e., a risky venture with no guaranteed return.
We examine the קֶרֶן הַצְּבִי with a light look at horns vs antlers and the Kaibab Deer experiment in the early 20th century.