Castoreum, a flavouring ingredient, comes from the two sacs between the anus and external genitals of male and female North American beavers. It's bitter, orange-brown, odiferous and oily.
Apart from its original purpose of marking territory (when mixed with urine), it's used in perfumes, in good company with another delightful animal product: ambergris, aka whale vomit.
Castoreum helps scent cigarettes and incense. And it's used to enhance the flavour of alcoholic and non-alcoholic beverages, baked goods, gelatins, puddings, soft and hard candies, frozen dairy products and chewing gum. Jamie Oliver told David Letterman it's used in vanilla flavouring in ice cream, but this has been disputed.
So which food products is it used in, specifically? No manufacturer will say, for obvious reasons.
Don't we have a legal right to know? Most certainly. But castoreum has been safely included, by the US Food and Drug Administration, in the umbrella category "Natural Flavor." No need to list any ingredients more specific than that.
Chapter 5 of Fast Food Nation expounds on the bizarre and shadowy world of Natural Flavors. We tend to think that food tastes like it does because the ingredients taste like they taste. But it ain't necessarily so, 
if we're talking processed foods, which soak up 90 percent of Americans' food budget.
A chemical additive provides the flavour. The majority of these are provided by a number of factories in New Jersey, which are highly secretive about their processes and clients' names. Author Eric Schlosser was allowed to tour several of these factories, and couldn't disclose specific brands, but he witnessed products of these types being flavoured: potato chips, corn chips, bread, crackers, cereal, pet food, ice cream, cookies, candies, toothpaste, mouthwash, antacids, popular soft drinks, sport drinks, bottled tea, wine cooler, all-natural juice drinks, organic soy beverages, beer and malt liquor.
There's also no legal obligation to disclose the components of a colouring agent. One such ingredient is cochineal extract, also called carmine or carminic acid (quick linguistic side note: the word "carminative" refers to something that makes you fart). As Schlosser describes, it comes from "the desiccated bodies of female Dactlyopius coccus Costa, a small insect harvested mainly in Peru and the Canary Islands." Seventy thousand of these creatures get ground up to make a pound of carmine, which helps make foods look pink, red and purple. Schlosser disclosed that this is used in Dannon strawberry yogurt, as well as Ocean Spray pink-grapefruit juice drink, and various frozen fruit bars, candies and fruit fillings.
I wish I could give you a specific list of where you might find castoreum, but none of my internet digging gave me anything more specific than repeated references to raspberry candies, and raspberry flavoured foods in general.
To paraphrase a bit from George Carlin's book When Will Jesus Bring the Pork Chops, if what you're looking for is raspberry flavour, you really can't do much better than eating some raspberries.
And maybe we should politely request our regulating bodies to let us know when we're ingesting crushed red bugs and/or the extract of a beaver's anus.
