frack rfack farck afrck rafck arfck frcak rfcak fcrak cfrak rcfak crfak facrk afcrk fcark cfark acfrk cafrk racfk arcfk rcafk crafk acrfk carfk frakc rfakc farkc afrkc rafkc arfkc frkac rfkac fkrac kfrac rkfac krfac fakrc afkrc fkarc kfarc akfrc kafrc rakfc arkfc rkafc krafc akrfc karfc frcka rfcka fcrka cfrka rcfka crfka frkca rfkca fkrca kfrca rkfca krfca fckra cfkra fkcra kfcra ckfra kcfra rckfa crkfa rkcfa krcfa ckrfa kcrfa fackr afckr fcakr cfakr acfkr cafkr fakcr afkcr fkacr kfacr akfcr kafcr fckar cfkar fkcar kfcar ckfar kcfar ackfr cakfr akcfr kacfr ckafr kcafr rackf arckf rcakf crakf acrkf carkf rakcf arkcf rkacf kracf akrcf karcf rckaf crkaf rkcaf krcaf ckraf kcraf ackrf cakrf akcrf kacrf ckarf kcarf
Note: these 'words' (valid or invalid) are all the permutations of the word frack. These words are obtained by scrambling the letters in frack.