My preliminary experiments with dictionary searching suggest that English has absolutely no words with roots of forms like *bobbib, *papoop, *tettit, *doded, *keckick, *gaggig, *mimmom, *naneen, *faffiff, *sussis, etc. These are simple CVCVC shapes that do not seem to contain any un-English sequence. They aren’t hard to say. In fact there is an example of a verb with the shape dVd that has a regular preterite tense: deed has the preterite deeded (as in The farmer deeded back his farm to the bank [WSJ w7_016]). But the pronounceability of deeded only makes the puzzle more acute: why are there no roots with the phonological form CiVCiVCi (where Ci is some specific consononant sounds and the V positions are filled with vowel sounds). Why? Or is the generalization perhaps wrong? Have I missed some words of the shape in question?