bkac kbac bakc abkc kabc akbc bkca kbca bcka cbka kcba ckba back abck bcak cbak acbk cabk kacb akcb kcab ckab ackb cakb
Note: these 'words' (valid or invalid) are all the permutations of the word bkac. These words are obtained by scrambling the letters in bkac.