shell hsell sehll eshll hesll ehsll shlel hslel slhel lshel hlsel lhsel selhl eslhl slehl lsehl elshl leshl helsl ehlsl hlesl lhesl elhsl lehsl shell hsell sehll eshll hesll ehsll shlel hslel slhel lshel hlsel lhsel selhl eslhl slehl lsehl elshl leshl helsl ehlsl hlesl lhesl elhsl lehsl shlle hslle slhle lshle hlsle lhsle shlle hslle slhle lshle hlsle lhsle sllhe lslhe sllhe lslhe llshe llshe hllse lhlse hllse lhlse llhse llhse sellh esllh slelh lselh elslh leslh sellh esllh slelh lselh elslh leslh slleh lsleh slleh lsleh llseh llseh ellsh lelsh ellsh lelsh llesh llesh hells ehlls hlels lhels elhls lehls hells ehlls hlels lhels elhls lehls hlles lhles hlles lhles llhes llhes ellhs lelhs ellhs lelhs llehs llehs
Note: these 'words' (valid or invalid) are all the permutations of the word shell. These words are obtained by scrambling the letters in shell.