bumf ubmf bmuf mbuf umbf mubf bufm ubfm bfum fbum ufbm fubm bmfu mbfu bfmu fbmu mfbu fmbu umfb mufb ufmb fumb mfub fmub
Note: these 'words' (valid or invalid) are all the permutations of the word bumf. These words are obtained by scrambling the letters in bumf.