Mishnà su Levitico 14:4

If it broke out covering all of his skin all at once: If this originated in a condition of cleanness, he is unclean; But if it originated in a condition of uncleanness, he is clean. One who becomes clean after having been isolated is exempt from the uncovering his head and rending his clothes, from shaving his hair and from bringing the birds. If he becomes clean after he had been certified unclean, he is liable to all these. Both convey uncleanness by entering.

With regard to the two birds: the commandment is that they be alike in appearance, in size and in price; and they must be purchased at the same time. But even if they are not alike they are valid; And if one was purchased on one day and the other the next they are also valid. If after one of the birds had been slaughtered it was found that it was not wild, a partner must be purchased for the second, and the first may be eaten. If after it had been slaughtered it was found to terefah, a partner must be purchased for the second and the first may be made use of. If the blood had been spilled out, the bird that was to be let go must be left to die. If the one that was to be let go died, the blood must be spilled out.