Sense Sonnet - Chiller

The Riddle of the Sphinx

What creature changes footing, so
At first has four, then two, then three.
Many a human does not know,
Though a "human" - the answer be.
Crawling as a babe on all fours,
Then walking older on two feet,
But with old age comes tores and wores,
A cane required for walk complete.
This is the Riddle of the Sphinx,
A mythical beast from the past -
Human with bird and lion links,
Who as on guard was unsurpassed.

Humans who got the riddle wrong
Did not remain live humans long.