retub ertub rteub treub etrub terub reutb erutb ruetb uretb eurtb uertb rtueb trueb ruteb urteb tureb utreb eturb teurb eutrb uetrb tuerb uterb retbu ertbu rtebu trebu etrbu terbu rebtu erbtu rbetu bretu ebrtu bertu rtbeu trbeu rbteu brteu tbreu btreu etbru tebru ebtru betru tberu bteru reubt erubt ruebt urebt eurbt uerbt rebut erbut rbeut breut ebrut berut rubet urbet rbuet bruet ubret buret eubrt uebrt eburt beurt ubert buert rtube trube rutbe urtbe turbe utrbe rtbue trbue rbtue brtue tbrue btrue rubte urbte rbute brute ubrte burte tubre utbre tbure bture ubtre butre etubr teubr eutbr uetbr tuebr utebr etbur tebur ebtur betur tbeur bteur eubtr uebtr ebutr beutr ubetr buetr tuber utber tbuer btuer ubter buter
Note: these 'words' (valid or invalid) are all the permutations of the word retub. These words are obtained by scrambling the letters in retub.