Next time you pick up a vanilla candy, think twice. A chemical compound used in vanilla flavored foods and scents comes from the butt of a beaver.

Castoreum comes from a beaver's castor sacs, located between the pelvis and base of the tail. Due to its proximity to the anal glands, the slimy brown substance is often mixed with gland secretions and urine.

"I lift up the animal's tail," Joanne Crawford, a wildlife ecologist at Southern Illinois University told National Geographic. "I’m like, 'Get down there, and stick your nose near its bum.'"

"People think I'm nuts," she added. "I tell them, 'Oh, but it's beavers; it smells really good.'"

Beavers use the brown slime, often compared to a thinner version of molasses, to mark their territory. The musky, vanilla scent is attributed to a beaver's diet of bark and leaves.

Manufacture have been using castoreum as an additive in foods and perfumes for at least 80 years, according to a 2007 study in the International Journal of Toxicology.

But getting a beaver to emit castoreum is not easy. Foodies are willing to "milk" the animals in order to get their hands on the gooey substance.

"You can milk the anal glands so you can extract the fluid," Crawford said. "You can squirt [castoreum] out. It's pretty gross."

Only 292-pounds per year is collected because the milking method is unpleasant for all parties involved.

And the worst part? The FDA-approved castoreum is not required to be listed as an ingredient on food items. Manufacturers may list "natural flavoring" instead.

Perhaps a bit too natural for us.