Castoreum, secretion from beaver anal glands, is legally classified as natural flavor and used in strawberry, raspberry, and vanilla flavorings. Manufacturers hide it from labels because consumers find the source disgusting, exposing how weird natural flavor regulations actually are.
It's the anal gland secretion of beavers. The actual legal definition of what passes as natural flavor is so convoluted. Basically, it's anything.
One of the most popular traded ones is beaver butt or strawberry.
Natural strawberry, natural raspberry, or natural vanilla could potentially be made from castoreum. I believe they don't put castoreum on the label because they don't want people to look it up and see what it is because it's kind of nauseating.
