firk ifrk frik rfik irfk rifk fikr ifkr fkir kfir ikfr kifr frki rfki fkri kfri rkfi krfi irkf rikf ikrf kirf rkif krif
Note: these 'words' (valid or invalid) are all the permutations of the word firk. These words are obtained by scrambling the letters in firk.