The word sphinx comes from the Greek verb σφίγγω: to squeeze or tighten up.
The Sphinx, part lion, part woman, may have wings, is a unique demon of destruction and bad luck.
Poised with a riddle, those who answered wrong were strangled and eaten by the ravenous monster so beware:
"Which creature has one voice and yet becomes four-footed and two-footed and three-footed?"
When Laius, King of Thebes, was killed in a road accident the Sphinx spotted a convenient dining opportunity. Sitting above Thebes on a cliff the sphinx asked all travellers her riddle, as none could answer she feasted heartily.
Oedipus (“Swollen Foot” *) solved the riddle answering: “It is Man who crawls on all fours as a baby, walks on two feet as an adult, and uses a walking stick in old age.”
In a fit of pique the Sphinx threw herself from her high rock and died… or ate herself, your choice. But she may have had the last laugh after all for Oedipus, his Mom, the rest of his family ... the whole citizenry of Thebes really, had a nasty run of bad luck.
(*S. Foot post, Sept.2/17.)