Have you ever said tock-tik or cross-criss? Probably not, because it sounds super weird. But why? When you repeat the same word but use a different vowel, it's called ablaut reduplication. Here are a few common examples: zig zig, clip clop, kit kat, ding dong, chit chat, tip top and flip flop. Starting to see a pattern?
The rule for ablaut reduplication goes like this: If there are two words, and the first word's interior vowel is an "I", the second word's vowel must be an "A" or "O". If there are three words, like bish-bash-bosh (a classic British phrase for all the Americans in the room) the sequence goes "I", "A", "O". What’s really strange is that you probably didn't learn this rule consciously. It’s just something you do automatically, and you learnt it from people who had no idea they were teaching it to you. There's no central theory as to why this happens. But experts believe it might have something to do with how our tongues form words - the series of vowels must be more natural on the muscles of the mouth and throat. ...Or we're living in a computer simulation and it's a glitch in the code. Neo, is that you?
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Image by Amador Loureiro