Four, not five trochees!
Shakespeare in this famous quote "Eye of Newt, and Toe of Frog..." uses a different pattern of rhythm to distinguish the witches' style of speech from the others. Instead of his usual Iambic pentameter that he uses for the nobles of Scotland and verse for the commoners, he goes about the Trochaic Tetrameter pattern for the three witches.
The dialog from the second witch among the three, on the commencement of the first act of the fourth chapter of Shakespeare's work, 'Macbeth', is a famous quote used by many to highlight witchcraft and situations associated with it. Citations of this quote can be found in many instances such as its mention in the fantasy novel 'Glory Road' (2006) and in the comical romance 'Practical Magic' (1998). These references hold good to a certain extent as and where the scene or act of a recipe is being involved. Most of the readers, however, ponder over the exact meaning of the quote and try to read between the lines. Let us get to know the dialog better, and hence, the 'quote' better.
William Shakespeare
William Shakespeare
The Cavern
In the opening scene of the fourth act of 'Macbeth', the curtain rises to reveal a dark cavern. Although there is light, but the air is creepy around it. There, in the middle of the cavern, are three witches, chanting and dancing to a rhythm, preparing the evil potion to which Macbeth is a witness. The dreaded mix boils and churns with great vigor, as the three witches perform the needful to create the spell. They throw in strange assortment of stuff into it and chant along as the potion brews to describe what's going in it and what forthcoming events 'the mix' is to behold upon the land of Macbeth. The charm being prepared is to trick Macbeth into apparitions that will bind him into a haughty sense of security and eventually lead to his doom.
The Chant
The witches observe the most appropriate time to start the 'preparation'. The first witch starts with throwing in a dangerously poisonous toad in the cauldron. They all sing to the heinous glory of the spell they are about to create to bring upon twice the 'trouble' with that curse. The second witch then sings out loud in a fashion that is both rhythmic, but highly scary (supposedly).
"Fillet of a fenny snake,
In the caldron boil and bake;
Eye of newt, and toe of frog,
Wool of bat, and tongue of dog,
Adder's fork, and blind-worm's sting,
Lizard's leg, and owlet's wing,
For a charm of powerful trouble,
Like a hell-broth boil and bubble."
Literal Meaning
The meaning of this dialog can be regarded literally, which would be quite obnoxious, but of course adds on to the scary index of the scene. A fillet from the fenny snake is getting stewed in the cauldron. The other inputs are the eye from the Newt (a kind of snake), a toe cut out of a frog, wool scraped off a bat, the tongue pulled out of dog, the snipped fork of the adder, and the sting of a burrowing worm. A leg clipped off a lizard and the wing torn away from an owl, all these go in to make the charm more powerful. The contents of the cauldron simmer and sputter like boiling in hell itself.

Although, with Shakespeare's intense love for symbolism and hidden intent, it becomes too difficult not to get intrigued by the strange nature of the contents. The underlying meaning of the dialog can be revisited with a different perspective and all the reader's imagination that can be put in.
Associated Allegories
The components required to cast a spell are usually of a specific value to balance the 'equivalent exchange' from the universe. The amount of soul you 'spend' to bring life to your cruel intent reflects in the type of items involved in that spell. In a more general sense, the method of acquiring the elements involved, sends your soul from being temporarily evil to a dark vacuum beyond the 'moral event horizon', and then there is no turning back to the goodness of humanity. This dialog can, therefore, be seen as the lowering of a soul in the darkness of evil in order to pursue higher powers.

Many explore further to realize that the variety mentioned is not actually what it 'sounds'. The 'eye of newt', for instance, is a mustard seed according to some of the herbalists. Similarly, 'Adder's tongue is a plantain, 'wool of bat' is moss, 'tongue of a dog' is a Hounds-tongue plant, 'toe of frog' is a bulbous buttercup, and 'owlet's wing' is just Goose-grass. The alternative images that the writer chose to portray could be owing to the petrifying aura that he wanted to build during the act.

Now, here lies two different allegories. First, the dialog speaks of a mystic spell that has been well hidden with words by the writer for its safekeeping. Second, the witches use the ingredients just to build a delusional environment that had sent Macbeth into hallucinating about the apparitions he had experienced.

Most importantly, the dialog is symbolic of all the evil these petty ingredients had brought upon the mental force of the valiant warrior Macbeth, which had turned him evil and into 'the hands and course' of his own doom.

The usage of the quote is reflected in the manner it is chanted. To create a profound imagery of witchcraft, it may be sung in deep and drowning tones. On the other hand, the narration of the chant to a child would involve sort of 'silly sing-along tone'.