ntfos tnfos nftos fntos tfnos ftnos ntofs tnofs notfs ontfs tonfs otnfs nfots fnots nofts onfts fonts ofnts tfons ftons tofns otfns fotns oftns ntfso tnfso nftso fntso tfnso ftnso ntsfo tnsfo nstfo sntfo tsnfo stnfo nfsto fnsto nsfto snfto fsnto sfnto tfsno ftsno tsfno stfno fstno sftno ntosf tnosf notsf ontsf tonsf otnsf ntsof tnsof nstof sntof tsnof stnof nostf onstf nsotf snotf osntf sontf tosnf otsnf tsonf stonf ostnf sotnf nfost fnost nofst onfst fonst ofnst nfsot fnsot nsfot snfot fsnot sfnot nosft onsft nsoft snoft osnft sonft fosnt ofsnt fsont sfont osfnt sofnt tfosn ftosn tofsn otfsn fotsn oftsn tfson ftson tsfon stfon fston sfton tosfn otsfn tsofn stofn ostfn sotfn fostn ofstn fsotn sfotn osftn softn
Note: these 'words' (valid or invalid) are all the permutations of the word ntfos. These words are obtained by scrambling the letters in ntfos.