Clack-click? Flop-flip?

English is endlessly fascinating, at least to me. So are the brains that master a zillion linguistic rules without knowing they exist. Consider these words or phrases (for today’s purposes, let’s not quibble the hyphens):

            Chit-chat                              Clip-clop
            Click-clack                            Criss-cross                  
            Dilly-dally                              Ding-dong      
            Knick-knack                         Flip-flop
            Mish-mash                           Hip-hop
            Pitter-patter                         Ping-pong
            Riff-raff                                  Sing-song                                                                               
            Wishy-washy                       Tick-tock
            Zig-zag                                  Tip-top

We learn in school about rhyme and alliteration, but who teaches about word pairs where only the vowel changes? The vowels must follow a particular sequence:
i before a, or i before o. Can you think of any common such pairing in which the order is reversed?

Small wonder learning or teaching English as a second language is so challenging. Here’s an entertaining read about how this vowel-order rule bumps up against another linguistic sequencing rule you may not have known you knew.