ferns efrns frens rfens erfns refns fenrs efnrs fners nfers enfrs nefrs frnes rfnes fnres nfres rnfes nrfes ernfs renfs enrfs nerfs rnefs nrefs fersn efrsn fresn rfesn erfsn refsn fesrn efsrn fsern sfern esfrn sefrn frsen rfsen fsren sfren rsfen srfen ersfn resfn esrfn serfn rsefn srefn fensr efnsr fnesr nfesr enfsr nefsr fesnr efsnr fsenr sfenr esfnr sefnr fnser nfser fsner sfner nsfer snfer ensfr nesfr esnfr senfr nsefr snefr frnse rfnse fnrse nfrse rnfse nrfse frsne rfsne fsrne sfrne rsfne srfne fnsre nfsre fsnre sfnre nsfre snfre rnsfe nrsfe rsnfe srnfe nsrfe snrfe ernsf rensf enrsf nersf rnesf nresf ersnf resnf esrnf sernf rsenf srenf ensrf nesrf esnrf senrf nserf snerf rnsef nrsef rsnef srnef nsref snref
Note: these 'words' (valid or invalid) are all the permutations of the word ferns. These words are obtained by scrambling the letters in ferns.