Animalic was a rudimentary private language invented by Mary and Marjorie Incledon, Tolkien's young cousins, about 1905. Tolkien, then in his early teens and already deep into Latin and Anglosaxon, found it amusing and learnt it. The sole surviving fragment of Animalic is the sample sentence given by Tolkien in The Monsters and the Critics p. 200: Dog nightingale woodpecker forty, meaning "you are an ass", ass being the animal and nothing else. Forty was Animalic for "ass, donkey", while donkey was the word for 40!
It appears that Animalic was a rather clumsy language; certainly it wasn't rational that extremely frequent grammatical words like "are" or the article "a(n)" were rendered by long words like nightingale and woodpecker. (I guess the Animalic word for "the" was *hippopotamus or something like that.) We shall never know how much Animalic Mary and her sister made, but it probably wasn't enough to translate the works of Shakespeare. Likely it was just a game; perhaps the kids decided upon words for "idiot", "moron" and the like, and then sat for hours throwing insults at one another: *Dog nightingale woodpecker horse! *Dog nightingale woodpecker hundred! *Dog nightingale woodpecker brontosaurus! (Slightly worried parent: "Hey, kids, what are you saying?" Innocent-looking children: "Nothing, mom! (Giggle.) Nothing at all!")
Tolkien's judgement is harsh, but justified: Animalic was "crude...in the extreme". (MC:200) Nontheless it was one of his very first acquintances with an invented language, perhaps the first. And it was to give way to Nevbosh - the first invented language Tolkien himself contributed to.