Archangel Singer,
First, let's talk terminology.
Deer's Tongue Leaf is a plant. The plant does have a root, as you noted, but we use the leaves, not the root, in our work. The shape of the leaves resembles the tongue of a deer, hence the name. We are relating the tongue-shaped leaf to eloquence.
Here is the plant:
And here is a Lucky Mojo packet of Deer's Tongue Leaf:
We use the leaves of this plant to increase the powers of speech because the leaf looks like a tongue. This form of magic is sometimes referred to as the Doctrine of Signatures. See my book "Hoodoo Herb and Root Magic" for more about the idea that the shape of a plant is God's way of giving os a clue about how to use it in medicine or magic.
There is a brand of German milk chocolate called Cat's Tongues (Katzen Zunger)) -- but nobody thought they were cut off of cats. Look! Here's a box -- my grandmother gave me these every year, in a box just like this!
There is also a kind of French cookie called Cat's Tongues (Langue du Chat) -- and here is a picture of them, too:
So a name is just a name.
Okay, then lets go on to the question of why an animal's tongue is used to stop gossip or to win a court case:
The reason is that by BINDING the tongue, you bind the words of the enemy or opponent. It's as simple as that. Filling it with hot pepper, filling it with poppy seeds, pinning it closed, tying it closed, freezing it, cooking it, eating it -- all of those actions, and similar variations of the tongue spell, are used to STOP THE SPEECH of an enemy or opponent.
Do you need a beef tongue exclusively, as Aura surmised, based on my web page?
No you do not.
A lamb tongue, a kid tongue, a veal tongue, a pig tongue, or a deer tongue will work just fine!
It's about the tongue being from a prey animal -- hence the magician's victory over the opponent's or enemy's power of speech. It is not about the species so much, and, again, the tongue DOES symbolize speech and eloquence in this spell as well, but instead of carrying it with you to have great speech, you symbolically name it for your enemy or opponent and then torture it and bind it, to limit the enemy's or opponent's eloquence.
At my Southern Spirits web site i have hosted a great description of the use of tongue spells in court cases, as given to the folklorist Alan Lomax by the renowned Creole jazz musician Jelly Roll Morton of New Orleans, Louisiana. As you read this, please note that the tongues are from varied species of animals (Morton specifically mentions lamb tongues and veal tongues).
LIBRARY OF CONGRESS NARRATIVE:
FERDINAND "JELLY ROLL" MORTON Born in Gulfport, Lousiana, 1890.
Interview conducted by Alan Lomax for the Library of Congress, 1938.
http://www.southern-spirits.com/morton- ... leans.html
Please so take the time to read this entire page. It is very interesting, and should prove educational to all.