And at the risk of sounding like Andy Rooney on Sixty Minutes, have you ever wondered why we say fiddle-fiddle and not fiddle- fiddle? Why is it ping-pong and pitter-patter rather than pong-ping and pitter-patter? Why ribs and drabs, rather than vice versa? Why can't a kitchen be spanned and spic? Whence riffraff, mishmash, flimflam, chit-chat, tit-for-tat, knick-knack, zigzag, sing-song, ding-dong, King Kong, crisscross, hilly-shally, see-saw, heehaw, flip-flop, hip pity-hop, ticktock, tic-tac-toe, deny-meeny-miney-moe, bric-a-brac, click-clack, hickory-hickory-dock, kit and caboodle, and Babbitt-bobbity-boo? The answer is that the vowels for which the tongue is high and in the front always come before the vowels for which the tongue is low and in the back.

The Language Instinct: How the Mind Creates Language