The Hebrew word for "atonement" (kippur) literally means "a covering" but in the context of the Levitical priesthood and sacrifices it has to do with ritual cleansing. The root word, kopher, means "a ransom". The "kippur"/atonement offerings are literally the ransom or price of ritual cleansing... and that ransom involves blood.
In Leviticus 14:52 the blood of a bird is used to cleanse a house with "leprosy":
Yom Rishon, 27 Nisan, 5784
Sunday, May 05, 2024 - Cinco de Mayo