I collect and read grimoires - books of spells, invocations, and magical instructions. My focus is on early modern European grimoires in the Christian tradition.
As I read, I index the information in these grimoires into the graph database behind Grimoire.org. Many spells (not to mention demons, fairies, miscellaneous bits of metadata, et cetera) appear in multiple grimoires, and the edges of the graph highlight these connections between books.
One such connection which I have discovered in the course of my reading is a very particular way of using a bird's tongue for magical ends.
Consider these spells:
Take the tongue of a vulture, lay it for three days and three nights in honey, afterward under your tongue, and thus you will understand all the songs of birds.
A turkey vulture's tongue (source)
Take feathers from a rooster's tail, press them three times into her hand. Probatum.
Or: Take a turtle dove tongue into your mouth, talk to your friend agreeably, kiss her and she will love you so dearly that she cannot love another.
Both of these spells are from The Egyptian Secrets of Albertus Magnus, a grimoire that is neither Egyptian nor connected to Albertus Magnus, but rather a German spell-book which first appeared in Cologne in 1725.
Here are a couple more spells:
When you are attending judicial proceedings, place a swallow's tongue under your tongue. The case will go in your favor.
Take the heart from a swallow and spear it on a stick. Then take the tongue of the swallow and place it under your tongue. Then display the swallow's heart. When someone is angry at you, display the swallow's heart, then place the bird's tongue under your tongue and speak to him. His anger will stop.
A hummingbird tongue (source)
Although these are distinct spells, with different outcomes and somewhat varied rituals, the similarity is striking. A bird's tongue is placed under ones own tongue, invoking the magician with magically enhanced powers of speech.
This is a classic case of sympathetic magic, a term coined by Sir James George Frazer in The Golden Bough. As he describes it:
If we analyze the principles of thought on which magic is based, they will probably be found to resolve themselves into two: first, that like produces like, or that an effect resembles its cause; and, second, that things which have once been in contact with each other continue to act on each other at a distance after the physical contact has been severed.
The Oxford English Dictionary has a more concise definition:
Primitive or magical ritual using objects or actions resembling or symbolically associated with the event or person over which influence is sought.
It makes sense, given this principal, that a bird's tongue can confer the extraordinary vocal ability of the bird to a human; like produces like.
Why do both these grimoires, which are otherwise quite different, share this particular technique? It may be that the author of the Black Books had read Egyptian Secrets, or it may have reached both authors through the oral tradition of folk magic. It may not be possible to say for sure where the idea first originated, or precisely how it was spread.
At any rate, if anyone out there does try to speak in court with a swallow's tongue under their own, I would like to wash my hands of all responsibility, and beg them to tell me how it goes.
The natural story of bird tongues is no less interesting than the supernatural one. I recommend Laura Erickson's exploration of the varied anatomy and function of bird tongues. And if you enjoy that, you may also enjoy another hyper-specific bird-related book, Feathers by Thor Hanson.