fstw sftw ftsw tfsw stfw tsfw fswt sfwt fwst wfst swft wsft ftws tfws fwts wfts twfs wtfs stwf tswf swtf wstf twsf wtsf
Note: these 'words' (valid or invalid) are all the permutations of the word fstw. These words are obtained by scrambling the letters in fstw.