heck ehck hcek chek echk cehk hekc ehkc hkec khec ekhc kehc hcke chke hkce khce ckhe kche eckh cekh ekch kech ckeh kceh
Note: these 'words' (valid or invalid) are all the permutations of the word heck. These words are obtained by scrambling the letters in heck.