On a holiday one is forbidden to eat doves found in a coop unless they have been designated before the holiday for consumption. What is the rule if one designated black doves and white doves for purposes of holiday consumption, but when he went to eat them he found that the black doves were in the place of the white doves, and vice versa? May one eat the doves on the holiday or not? What are the issues under debate? On one hand, there is reason to think that the doves found in the coop are the doves which were designated before the holiday for consumption but they switched places, and so they are permissible for consumption. On the other hand, there is reason to think that the doves which had been designated for eating flew the coop and that the doves which are now in the coop are other doves, ones which had not been designated for eating, and so they are forbidden for consumption. (The Talmud rules that they are prohibited; the doves which had been designated flew the coop and the present doves are different ones.)
(Babylonian Talmud Tractate Beitzah 10b)