You’ve been using it all your life. It’s just that you’ve never heard of it. But if somebody said the words zag-zig, or ‘cross-criss you would know, deep down in your loins, that they were breaking a sacred rule of language. You just wouldn’t know which one.
All four of a horse’s feet make exactly the same sound. But we always, always say clip-clop, never clop-clip. Every second your watch (or the grandfather clock in the hall makes the same sound) but we say tick-tock, never tock-tick. You will never eat a Kat Kit bar. The bells in Frère Jaques will forever chime ‘ding dang dong’.
Reduplication in linguistics is when you repeat a word, sometimes with an altered consonant (lovey-dovey, fuddy-duddy, nitty-gritty), and sometimes with an altered vowel: bish-bash-bosh, ding-dang-dong. If there are three words then the order has to go I, A, O. If there are two words then the first is I and the second is either A or O. Mish-mash, chit-chat, dilly-dally, shilly-shally, tip top, hip-hop, flip-flop, tic tac, sing song, ding dong, King Kong, ping pong.
Why this should be is a subject of endless debate among linguists, it might be to do with the movement of your tongue or an ancient language of the Caucasus. It doesn’t matter. It’s the law, and, as with the adjectives, you knew it even if you didn’t know you knew it. And the law is so important that you just can’t have a Bad Big Wolf.