sifer isfer sfier fsier ifser fiser siefr isefr seifr esifr iesfr eisfr sfeir fseir sefir esfir fesir efsir ifesr fiesr iefsr eifsr feisr efisr sifre isfre sfire fsire ifsre fisre sirfe isrfe srife rsife irsfe risfe sfrie fsrie srfie rsfie frsie rfsie ifrse firse irfse rifse frise rfise sierf iserf seirf esirf iesrf eisrf siref isref srief rsief irsef risef serif esrif sreif rseif ersif resif iersf eirsf iresf riesf erisf reisf sferi fseri sefri esfri fesri efsri sfrei fsrei srfei rsfei frsei rfsei serfi esrfi srefi rsefi ersfi resfi fersi efrsi fresi rfesi erfsi refsi ifers fiers iefrs eifrs feirs efirs ifres fires irfes rifes fries rfies ierfs eirfs irefs riefs erifs reifs feris efris freis rfeis erfis refis
Note: these 'words' (valid or invalid) are all the permutations of the word sifer. These words are obtained by scrambling the letters in sifer.