birks ibrks briks rbiks irbks ribks bikrs ibkrs bkirs kbirs ikbrs kibrs brkis rbkis bkris kbris rkbis krbis irkbs rikbs ikrbs kirbs rkibs kribs birsk ibrsk brisk rbisk irbsk ribsk bisrk ibsrk bsirk sbirk isbrk sibrk brsik rbsik bsrik sbrik rsbik srbik irsbk risbk isrbk sirbk rsibk sribk biksr ibksr bkisr kbisr ikbsr kibsr biskr ibskr bsikr sbikr isbkr sibkr bksir kbsir bskir sbkir ksbir skbir iksbr kisbr iskbr sikbr ksibr skibr brksi rbksi bkrsi kbrsi rkbsi krbsi brski rbski bsrki sbrki rsbki srbki bksri kbsri bskri sbkri ksbri skbri rksbi krsbi rskbi srkbi ksrbi skrbi irksb riksb ikrsb kirsb rkisb krisb irskb riskb isrkb sirkb rsikb srikb iksrb kisrb iskrb sikrb ksirb skirb rksib krsib rskib srkib ksrib skrib
Note: these 'words' (valid or invalid) are all the permutations of the word birks. These words are obtained by scrambling the letters in birks.