birk ibrk brik rbik irbk ribk bikr ibkr bkir kbir ikbr kibr brki rbki bkri kbri rkbi krbi irkb rikb ikrb kirb rkib krib
Note: these 'words' (valid or invalid) are all the permutations of the word birk. These words are obtained by scrambling the letters in birk.