backs abcks bcaks cbaks acbks cabks bakcs abkcs bkacs kbacs akbcs kabcs bckas cbkas bkcas kbcas ckbas kcbas ackbs cakbs akcbs kacbs ckabs kcabs bacsk abcsk bcask cbask acbsk cabsk basck absck bsack sback asbck sabck bcsak cbsak bscak sbcak csbak scbak acsbk casbk ascbk sacbk csabk scabk baksc abksc bkasc kbasc akbsc kabsc baskc abskc bsakc sbakc asbkc sabkc bksac kbsac bskac sbkac ksbac skbac aksbc kasbc askbc sakbc ksabc skabc bcksa cbksa bkcsa kbcsa ckbsa kcbsa bcska cbska bscka sbcka csbka scbka bksca kbsca bskca sbkca ksbca skbca cksba kcsba cskba sckba kscba skcba acksb caksb akcsb kacsb ckasb kcasb acskb caskb asckb sackb csakb scakb akscb kascb askcb sakcb ksacb skacb cksab kcsab cskab sckab kscab skcab
Note: these 'words' (valid or invalid) are all the permutations of the word backs. These words are obtained by scrambling the letters in backs.