kbru bkru krbu rkbu brku rbku kbur bkur kubr ukbr bukr ubkr krub rkub kurb ukrb rukb urkb bruk rbuk burk ubrk rubk urbk
Note: these 'words' (valid or invalid) are all the permutations of the word kbru. These words are obtained by scrambling the letters in kbru.