tvrd vtrd trvd rtvd vrtd rvtd tvdr vtdr tdvr dtvr vdtr dvtr trdv rtdv tdrv dtrv rdtv drtv vrdt rvdt vdrt dvrt rdvt drvt
Note: these 'words' (valid or invalid) are all the permutations of the word tvrd. These words are obtained by scrambling the letters in tvrd.