ursid rusid usrid surid rsuid sruid urisd ruisd uirsd iursd riusd irusd usird suird uisrd iusrd siurd isurd rsiud sriud risud irsud sirud isrud ursdi rusdi usrdi surdi rsudi srudi urdsi rudsi udrsi dursi rdusi drusi usdri sudri udsri dusri sduri dsuri rsdui srdui rdsui drsui sdrui dsrui urids ruids uirds iurds riuds iruds urdis rudis udris duris rduis druis uidrs iudrs udirs duirs idurs diurs ridus irdus rdius drius idrus dirus usidr suidr uisdr iusdr siudr isudr usdir sudir udsir dusir sduir dsuir uidsr iudsr udisr duisr idusr diusr sidur isdur sdiur dsiur idsur disur rsidu sridu risdu irsdu sirdu isrdu rsdiu srdiu rdsiu drsiu sdriu dsriu ridsu irdsu rdisu drisu idrsu dirsu sidru isdru sdiru dsiru idsru disru
Note: these 'words' (valid or invalid) are all the permutations of the word ursid. These words are obtained by scrambling the letters in ursid.