excr xecr ecxr cexr xcer cxer exrc xerc erxc rexc xrec rxec ecrx cerx ercx recx crex rcex xcre cxre xrce rxce crxe rcxe
Note: these 'words' (valid or invalid) are all the permutations of the word excr. These words are obtained by scrambling the letters in excr.