In Genesis's Noah's Ark story, one pair of each animal not classified as clean entered the Ark.
Genesis 7:2–3 distinguishes between clean animals and other animals when describing who enters the Ark. Noah is told to take one male and one female of each kind in the latter category. This creates a numerical contrast with the seven pairs of clean animals.
Many popular versions of the story say that animals went into the Ark “two by two.” That phrase is memorable and accurate for the one-pair instruction, but it can obscure the separate count given for clean animals. The biblical text therefore contains more than one animal-entry number.
The passage does not define every animal using modern species terminology. “Clean” and “not clean” are categories in the biblical account, and the narrative later gives special attention to clean animals when Noah makes an offering after the Flood.