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