nderf dnerf nedrf endrf denrf ednrf ndref dnref nrdef rndef drnef rdnef nerdf enrdf nredf rnedf erndf rendf dernf edrnf drenf rdenf erdnf rednf ndefr dnefr nedfr endfr denfr ednfr ndfer dnfer nfder fnder dfner fdner nefdr enfdr nfedr fnedr efndr fendr defnr edfnr dfenr fdenr efdnr fednr ndrfe dnrfe nrdfe rndfe drnfe rdnfe ndfre dnfre nfdre fndre dfnre fdnre nrfde rnfde nfrde fnrde rfnde frnde drfne rdfne dfrne fdrne rfdne frdne nerfd enrfd nrefd rnefd ernfd renfd nefrd enfrd nferd fnerd efnrd fenrd nrfed rnfed nfred fnred rfned frned erfnd refnd efrnd fernd rfend frend derfn edrfn drefn rdefn erdfn redfn defrn edfrn dfern fdern efdrn fedrn drfen rdfen dfren fdren rfden frden erfdn refdn efrdn ferdn rfedn fredn
Note: these 'words' (valid or invalid) are all the permutations of the word nderf. These words are obtained by scrambling the letters in nderf.