sofur osfur sfour fsour ofsur fosur soufr osufr suofr usofr ousfr uosfr sfuor fsuor sufor usfor fusor ufsor ofusr fousr oufsr uofsr fuosr ufosr sofru osfru sforu fsoru ofsru fosru sorfu osrfu srofu rsofu orsfu rosfu sfrou fsrou srfou rsfou frsou rfsou ofrsu forsu orfsu rofsu frosu rfosu sourf osurf suorf usorf ousrf uosrf soruf osruf srouf rsouf orsuf rosuf surof usrof sruof rsuof ursof rusof oursf uorsf orusf rousf urosf ruosf sfuro fsuro sufro usfro fusro ufsro sfruo fsruo srfuo rsfuo frsuo rfsuo surfo usrfo srufo rsufo ursfo rusfo furso ufrso fruso rfuso urfso rufso ofurs fours oufrs uofrs fuors ufors ofrus forus orfus rofus frous rfous ourfs uorfs orufs roufs urofs ruofs furos ufros fruos rfuos urfos rufos
Note: these 'words' (valid or invalid) are all the permutations of the word sofur. These words are obtained by scrambling the letters in sofur.