pfft fpft pfft fpft ffpt ffpt pftf fptf ptff tpff ftpf tfpf pftf fptf ptff tpff ftpf tfpf fftp fftp ftfp tffp ftfp tffp
Note: these 'words' (valid or invalid) are all the permutations of the word pfft. These words are obtained by scrambling the letters in pfft.