The core movements of Wing Tsun chi sao are summarized in a practice called poon sao. Poon sao is chi sao where one refrains from any techniques and simply does the familiar rolling motions with a partner. Even within poon sao, there is room for a lifetime of practice.
Poon sao contains at three core principles: tan sao ("palm-up arm"), bong sao ("wing arm"), and fuk sao ("sensing arm"). These three techniques are often called the "seed techniques" of Wing Tsun/Chun.
In chi sao, perfect posture and sensitivity are everything. Any mistake in either category can be capitalized upon by a competent practitioner, and since a Wing Tsun stylist never strikes once, to be capitalized upon is to be defeated. Poon sao/chi sao is even more fun than it looks.
Your body is with-holding a thousand and one secrets from you. It knows more than you will ever learn. Practice chi sao, and it might let something slip.