Mishnah Kinnim 2:1: An unspecified pair of birds, from which one flew off, or that flew among birds designated to die, or if one of the pair died, a second bird should be bought for the remaining bird. If it flew off among birds that were set to be brought as sacrifices, it becomes invalid and invalidates its matching bird [the other bird of its pair], since a bird that flies away from its pair is invalid and makes its matching bird invalid.

קן סתומה שפרח ממנה גוזל לאויר. או שפרח בין המתות או שמת אחד מהן יקח זוג לשני. פרח לבין הקריבות פסול. ופוסל אחד כנגדו. שהגוזל הפורח פסול. ופוסל אחד כנגדו:

Mishnah Kinnim 2:2: How is it? If there are two women, this one has two pairs and this one has two birds and one bird flew from this woman's [pair] to the other woman's [pair] , it invalidates one bird by its leaving. If it then returned [to its original pair] it invalidates one by returning. If it flew back and forth multiple times it does not cause further invalidation since even if they are mixed up, there are at least two [valid] birds remaining.

כיצד שתי נשים. לזו שתי קנים. ולזו שתי קנים. פרח מזו לזו פוסל אחד בהליכתו. חזר. פוסל אחד בחזירתו. פרח וחזר. פרח וחזר. לא הפסיד כלום. שאפילו הן מעורבות אין פחות משתים: