If you have played the party game called “Pass the Secret”, you will know that by the time the message reaches back to you, it would have been distorted beyond recognition. But for many millennia, the Vedic hymns were memorized and handed down by word of mouth and the contents were preserved intact. The actual wording, intonation and pronounciation had to be perfect and for this the Vedic seers created a system to prevent alteration.
At Huffington Post, Suhag Shukla explains this system
To ensure that the Vedas remained unchanged in content, intonation, and inflection, a number of techniques of recitation with increasing complexity and difficulty were developed, including Jatapata.
The first is Samhita, the simplest form of recitation that approaches the mantra as it is, for example,”the sky is blue” (abcd). Next is Padha, where each word is broken down, as in, “the/sky/is/blue” (a/b/c/d). Krama, the third technique, adds the first real level of difficulty into the recitation through a pattern of “the sky/sky is/is blue” (ab/bc/cd). Jatapata, the first of the more challenging, alternates between a repetitious interposing and transposing of words to create a pattern of “the sky sky the the sky/sky is is sky sky is/is blue blue is is blue” (abbaab/bccbbc/cddccd). Between Jatapata and the last technique are six other techniques (called Mala, Shikha, Rekha, Dvaja, Danda and Ratha) that again are built-in combinations and permutations that have ensured that the order and words of the Vedas remain unchanged. The ultimate and most complex technique is called Ghanam. Its mind-boggling backwards and forwards pattern is, “the sky sky the the sky is is sky the the sky is/sky is is sky sky is blue blue is sky is blue” (abbaabccbaabc/bccbbcddcbcd).[Peeling Back the Layers of Sanskrit and Vedic Chanting]